I use my trailer to camp all year, plus hunting season. Which means it gets used in sub 20s weather. I've never winterized it be a use it get used so much.
1987 trailer, single pane windows. Never once thought it was too cold. Never had sweat on the windows. You gotta leave the roof vents open. Don't strive for 85 degrees inside, when it's 17 outside. I get it to about 68, vents open, no issues.
Yes, it goes through propane. But I've done the trials both ways. It's really not that much. Using it that way, and cooking and fridge too, I've never used up a whole 30lb tank in 7 days. Close, but not quite.