Real world cold testing
I have done some real world testing with my 2015 Expedition.
1. Carry some water in your tanks. Unless you invest in a heated water hose your hose may freeze. Take it off and drain it if you think freezing weather is coming. As long as you are using the gas heat in your MH there is some heat going into the water tank bay. Make sure you Propane tank is full when you start into cold weather.
2. Use your furnace and not a heat pump or fireplace to heat the coach when freezing. The reason related to the furnace heating the water compartment.
3. The weak point is the outside compartment where your water inlet, water pump etc. are located. Even when the water tank area is fine the outer area will freeze. I have had my hose freeze, hence the recommendation to carry internal water. water pump freeze (not good), the water pump hoses etc. I purchased a small ceramic space heater about the size of half a loaf of bread. I kept it on a low setting. I also placed a remote temperature sensing unit (cheap) to monitor what was going on.
4. Putting some insulation (Styrofoam, batting etc.) over the sink-like bays where your sewer hose and water hose enter the coach. Most of the heat escapes there according to the Fleetwood folks. I have successfully operated into single digits.