We live in our 305RL High Country fulltime and got down to 12 degrees this winter a couple of times and we faired pretty well. We do have an extra electric heater to go with the fireplace and only run the furnace at night a little to warm the under belly, As far as be insulated we are pretty happy with ours. Hope this helps.
2016 F-350 DRW 4x4
Anderson Ultimate Aluminum Hitch
2016 Montana High Country 305 RL with Mich. Ribs