Four season full timing in a fiver.

We camped year round in our Weekend Warrior, but are not full time. Ours had insulated tanks and belly but the windows were single pane with a reflective coating. Our open garage floor plan could be heated for two nights on one 30 lb cylinder, but the dual batteries had to be charged back up by the generator daily due to heater duty cycle. I'm sure most of our heat loss was through the rear ramp door and windows since they would sweat. Our walls, ceiling and floor were dry and comfortable. I did wrap all exposed pipe in foam which helped the most inside the storage areas and cabinets that did not get as much heat. Pulling in the slide did keep it warmer since the slide walls were not insulated.

Definitely choose dual pane windows and insulated underside if you plan to camp in bellow freezing weather. We always had water in the tanks and avoided using a tap since we did not have a heated supply hose. Only once the dump valves froze and I had to run the generator to thaw them with a hair drier at the dump station.