We keep camping until it either start freezing day and night or the heavy snows come. Our 3 season rig needs the warm up to keep from freezing up and I have no desire to pick my way along 10 miles of ruts after a foot of snow has come down.
Our first trip in late fall we tried to do it like a hard sided tent. We used the furnace at its lowest setting at night to keep us from freezing in the 26 degree temps. The only heat in the daytime came from cooking. We put rugs on the floor and at night put towels on the windows/ stuffed the vents to cut down on the heat loss. It wasn't too bad if it warmed up but on the 40* rainy days we stayed bundled up. When the battery ran low, I used the truck and jumper cables to keep it up. We were going to stay longer but caught a weather report calling for a foot of snow that night and without saying a word, both of us started packing up.
After that we decided we bought the trailer so that we didn't have to be cold and miserable. I added battery, got a generator and then solar. Last fall we had the same conditions and we set the stat at 74* and left it there.
BTW We tried to use a portable propane heater that first trip, luckily it was during the day. Even with four windows and a vent cracked it made me sick. There just isn't enough Oxygen above 7000 ft to use them safely and we were at 10,000 ft.