All of my camping is in the Sierra's or other back country area's.
The last 4 or 5 years I've camped at close to 9000 feet elevation due to the drought and a lack of snow.
Some of the trips were down to the mid 20's.
I had no problem with the standard Suburban that came with the trailer.
Between my down sleeping bag, a down comforter over that and a programmable thermostat that turned the
furnace on at 7 AM I was comfortable.
John