We dry camp in the Colorado Rockies in our pop-up starting in May. At night, the temps get down in the low 30's. We don't run heat at night and we don't run the generator for the electric mattresses.
The few times I have used the heat at night when the temps go into the 20's, the furnace almost never shuts off. I run the heat just to keep the water pipes from freezing at night. The heat just won't stay in the camper.
We use good sleeping bags and I crank the heat on in the morning to make it easier to get out of bed in the cold.
The daytime temps in May are in the 50's and 60's. It is worth putting up with a few hours of cold at night for the perfect daytime temps.
Larry