Per popular request, I have written up some of MY advice on cold weather, and I mean sub zero to single digits use of your coach. This is a whopper of a post. It documents MY methods and is not meant to inspire religious debate, just accept this is what I do. You may and probably will do things differently and that's great.
Note, the full extent of the following is for zero and below coach use as I do it. As you ease into the teens and then the twenties things get a whole lot more relaxed and simplified. So, the following are MY rules of near zero to sub zero engagement. Your rules will vary depending on your personal preferences and experiences.
First of all, sub zero is really no big deal if you know a) your limits and b) the coach limits ->IN ADVANCE<-. You need to be prepared and practiced and you need to do your own experiments in advance as every coach is different and you have to experiment with yours.
First off don't believe anything I write or anything anyone else writes at face value. This is only guideline information from which you can start. You have to do you own experiments with your own coach and your own personal limits. People and coaches are all very different. So here's some things that I do and follow. Again, no really big deal, but I ALWAYS know what I am getting into before I do it when dealing with such cold temperatures.
After Being Prepared, Keep It Simple is the next main ideal.
General Info:
1) Know cold weather "survival" for YOURSELF first and foremost – this is a whole 'nutter topic. Know your personal limits and do not exceed them. The more you do it the more you learn. Jumping in on the deep end is a path to disaster. Cold is different than hot and far more lethal.
2) Keep your CO AND LP detectors in tip top shape, yes BOTH.
3) If you are parked in a cold area, scope out accessible fuel sources and propane filling options. Get RV service phone numbers and taxi phone numbers in advance. Know what the local hardware store has in terms of supplies for the DIY'er. Check out the local auto and truck parts stores (if any) so you know what options you have. In the cold, time is of the essence; you can't put off fixing a critical component or miss a warmer weather window for a repair while looking for all this info.
4) Make sure your diesel tank is full of LOCAL fuel as cold weather additives are automatically added based on the local climate. My religious take is NOT to add anything to my fuel, you don't need to, KISS. This is what I do, please don't debate it. A disaster would be to fill up and drive from Arizona and then park in zero degree Colorado with a low tank of warm climate fuel. Besides, safety and comfort will dictate to always keep a FULL fuel tank in the coach and toad when driving subzero or snowy climates. You never know when you'll need it because of a highway closure. In addition, I will always keep a full water tank and empty grey/black while travelling just in case. So every time you can, KISS and just fill and dump, everything while travelling under difficult conditions!
5) Practice blow out winterization (it's fastest and least impactful if limited water to flush afterwards) and be prepared to do this in the cold in case your furnace breaks. Also keep a couple gallons of the pink stuff handy as extra insurance.
6) Get several remote sending thermometers, you must monitor a lot of places in your initial experiments to determine cold problem areas in your coach and then to continue to monitor critical areas while camped cold. You can begin your experiments in warmer temps by measuring what the different temps are all around your basement and utility bay as the days start to get chilly.
7) Understand the plumbing of your coach pay particular attention to how its routed as you have to know where trouble spots might be (exposed lines, outside wall lines, sags or elbows in lines that collect water, etc.). Open access covers and see how cold it gets in those tight areas.
8) Understand your furnace in every way, it's your key to success.
9) Keep snow and ice away from exhaust vents.
10) Note that sustained cold temps are a lot different and more problematic than overnight dips.
11) Think about and prepare what you'll do if the shore power goes out and you can't start your genset. You have limited battery life, what uses will you prioritize. When will you blow water lines, how will you yourself keep warm, what personal items will freeze in the coach and leak later (liquid soaps, deodorants, beverages, and the like). How will you protect yourself and then protect the coach.
12) Understand that closing up your slideouts may take days waiting for a thaw or sunshine as the slidouts might freeze, the awning toppers and covers might freeze. Be prepared for this. Or, don't use your slideouts if you'll be moving often.
13) Have back up space heaters... but remember you may not have shore power or be able to start the genset to use only electric ones. Have on hand an indoor certified propane powered heater as well – and the propane cylinders.
14) How will you start the big motor if you have too? No electricity means no electric block heat. What if you are dry camped and there is no shore power at all? If you have hydronic heat and it does not have the engine preheat pump PUT IT IN.
Click here for a tutorial. About $350 for parts and an hour or so of labor, everything is already there, just plug it in. Newmar does not install this option on HydroHot. Newmar Oasis units do have it I think. How are you going to move your beast if you can't preheat it at sub zero? Electric block heater is not usable if you don't have shore/genset power. I regularly (multi)overnight w/o genset in subzero and just leave the hydronic engine preheat running. Just an amp or so and the engine stays at 100 degrees+.
15) Things are brittle when cold and ice jams a lot of things. Don't force anything (slidouts, toppers, windows, etc.) Just don't use something that doesn't seem to be working right from the cold. Wait until the sun thaws it or you can manually thaw it. Or just don't use it in the first place. You are not in sunny Florida. No banging, no chipping as these actions surely will break things.
16) No hot water to thaw things, you'll only make things worse. Dry heat only (hairdryer, heatgun, sunshine, etc.).
17) If you need to, glue a small 12v tank heater pad underneath you entry steps to keep them ice and slip free.
18) KISS is the golden rule in the cold. Focus on the important, infinite hot water showers are potentially a luxury so skip leaving the water and sewer connected. Although you can heat tape inside a swim noodle these items but what an extra hassle when you already have a ton to worry about. I fill and dump as needed. Your coach is self contained for a reason!
19) BTW A Sanicon hose is infinitely a lot easier to manipulate in cold than the 3inch sewer frozen stiff plastic hose.
20) Test start your genset quite regularly in the cold. It is your first line of emergency backup. Know it's limits. So far, I know mine will start at -10F sustained temp without too much trouble, though it belches and coughs for a while. Unfortunately, there is no preheat option for your genset, it would have to be hydronic to make any sense. I may splice into the big motor preheat lines in the future to heat the genset from the hydronic too.
21) Don't deploy your automatic Motosat dish if you aren't prepared to get up on the slippery snow filled roof to unfreeze it when you want to put it down. Which also means you really need a means to access the roof to clear snow/ice if necessary.
22) Yep, you will HAVE to do many things a little differently at zero degrees than you would at 80. But, one thing is for sure, your drinks certainly will NOT need any ICE!
Here's some specifics for a Newmar Essex 4502 to consider:
NOTE ESSEX SPECIFIC INFO follows.
On this model the plumbing is all centrally located in the mid section of the coach – this is a plus as it is easier to keep track of the plumbing and to keep it warm. Know where all your plumbing is and how it runs.
Newmar installs a separate heat exchanger behind the water utilities panel on a separate rough thermostat – newer models have a fixed thermostat I think. This heat exchanger is key to keeping the coach operational in the very cold. Use your thermometers to monitor temps in this compartment in several areas both high and low and left and right to make sure you know what issues may exist. Then measure the rest of the basement areas to see what areas are colder than others to avoid storing freezable items in the colder areas. You don't need to crank this thermostat to the max, just figure out what is warm enough for the current conditions to keep all areas of the utility bay above 32 degrees. I have mine set for about 35 degrees. My thermostat bulb is located on the bottom right floor of the bay and hence registers a whole lot colder than the rest of the bay. The Manibloc area of my bay will be nearly 70 degrees while the register is operating. Keep monitoring this bay while cold camped, it's the heart of you plumbing survival. The very forward door side bay is my coldest with temps hitting 30-32 when outside is at a sustained zero. The rest of the basement is above 32.
Some Eplex systems in these coaches may not activate any heat if set to less than 55 degrees. Test your Eplex thermostat zones out by setting them below this setting. This is a programming glitch and can be fixed by Newmar.
My LP Norcold refer has the only problem water pipe which is the ice maker feed line to the solenoid. The rest of the icemaker lines are heat taped allegedly to 0 degrees. KISS says to just turn off the feed line valve at the under sink filter and drain the icemaker/water tap for the winter. Otherwise, you'll have to heat tape the feed line up to and including the solenoid and then test the existing after solenoid heat taped lines.
Use no awnings – this is a recipe for disaster and besides, the sun is free heat and will be very useful. The slide toppers can not be disengaged. You'll need them to keep snow off the slideout anyway. I may clear off the toppers IF the weather is going to go above freezing for a couple days and is enough to melt them clear. Otherwise, leave them alone until you begin preparations to move.
I have found that my MotorAide feature of the HydroHot simply can not keep up while driving in single digit temps. Hence, the automatic "low temp shutoff" feature of the HydroHot kicks in and the utility bay register (and all the rest) naturally shut off until the MotoAide catches up. Yep, I slushed up my utility bay plumbing before discovering this issue. Solution, simple, drive with the HydroHot burner ON while in near zero conditions. Fortunately, slush isn't frozen solid and I had no damage.
You'll need to close the front privacy shade during uber-cold if the front area of the coach is to stay reasonably warm. It acts as a wonderful air cushion insulation blanket. Otherwise, you'll need to run a single space heater up front usually on low to help out with that massive heat loss Imax window when temps sustain single digits or below. The front register simply can not keep up at those temps. Park that Imax facing due south and that will help a whole lot!
In addition partially closing (8 inches or so) the door side privacy shade will help insulate the Zone 1 thermister located there and prevent erroneous readings on your Zone 1 heat.
If my furnace fails I have tested my coach and found that 2 space heaters and an electric blanket upstairs and one carefully positioned space heater in the utility bay on low will keep me going until I lose shore power. You need to test what you and your coach needs in this scenario and can do this in your driveway before hitting the road. If there is no shore power and I can't start the genset then I'll blow the water lines and fire up the propane indoor certified heater and figure out my next steps.
Notice how often I repeat the notion of "try this at home before hitting the road?" Heed that advice. Be prepared. Have a plan (or at least have thought about) what to do in every contingency.
Well, there's some initial thoughts. I am sure I have missed writing a lot of stuff. Depending how this thread goes I might update this master list.
Happy cold camping, it is a wonderful experience with unmatched beauty.
Additions:
One other thought is to make sure your coach air line dryer system (be it a desiccant filter like Spartan uses or an alcohol injection system) is in tip top shape. If it freezes you won't be stopping - ice or no ice. Especially check the desiccant filter system's electric heater functionality.
, I added it to the Quick Tips file. 
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