We did it for one winter about 10 years ago, and let me tell you it ain't fun.
I am not familiar with the trailer you have in mind but what the salesman tells you about R40 insulation that is 'bull'.
We had a 29' Vanguard Legend 5th wheel at the time and had the dealer (Tailblazer RV) spray foam the entire bottom of the trailer, they installed heat pads under the tanks and wrapped the freshwater lines as well as the drain lines in tin foil then heat tape then insulation. We also had double pane windows installed. You can not leave any hose outside for more than a few minutes at most, sewer or fresh water.
You need to have a spot out of the wind, inside a shed would be better but you need sunlight to keep your sanity, the days are short enough in the winter already.
We ended up putting plastic film over the windows to keep condensation in check but you need to keep one roof vent cracked open ever so slightly to let moisture escape. We did run into problems when the cable to dump the tanks froze up on us, I don't remember how we solved that.
Oh, and ask for a volume discount on propane, because you're gonna need a lot. If I had to do it again, I would put skirting around the entire trailer and place an electric heater under the trailer. Remember in the old days when they lit a fire under the tractor (or truck) to thaw the oil so the engine would turn over?
I almost forgot, you need an electric heater in your front storage compartment on thermostat and find a way to run the furnace fan continuously at slow speed. Don't listen when someone tells you a 60 Watt light bulb is enough in the storage bay - it is not! Place thermometers with remote readouts in all critical areas, like in the storage bay, on the ground, under the kitchen sink, under the bathroom sink - you get the idea. Let the snow accumulate around the trailer skirting, not so high that it reaches the trailer side walls of course and get mouse traps, you're gonna need them.
Travelaire in Red Deer used to build trailers specifically for the north, but they are long gone. If I had to do it again, I would go to Tee Pee Trade & RV Centre
in Camrose, they sell the Excel which is highly rated by fulltimers. Talk to Rob, he is the owner and deals with this on a daily basis.
Hope this helps and keep us posted.