Just returned from a trip including 3 nights in AZ's high desert with overnight temps at or just above freezing. Had shore power all 3 nights - windy 1st night, ran furnace a fair bit, were still cold (older, thin cotton flannel sheets / 2 comforters on bed). Switched to fleece sheets 2nd night, left furnace on with thermostat on lowest setting, were very comfortable. Only significant air cold air leakage was at the separation between upper and lower sections of the door, rolled a fleece blanket & laid it in the joint on the inside of the door, made a big difference.
Spent 3 nights on the central CA coast on the way home (overnight temps in the upper 40's), weren't aware of the furnace coming on at anytime overnight - started the trip with both propane tanks full and only used about half of one tank. In the future, will probably use a compact electric heater when we have shore power - no point in burning propane unnecessarily....