Ever heat your camper with a hair dryer? An electric heater draws about 1500 watts or about half the power available in most hybrids with 30amp service. And, guess what? The typical hair dryer is the same 1500 watts. As is the "heat strip" on some AC units like we had on our popup. None of these do a good job of heating a camper.
We run the propane furnace which puts out much more heat and supplement this with the space heater which maintains cabin temperatures well once it's warm.
Beware. Propane furnace burns a pound of fuel every hour of flame time. 20 pound tank? 20 hours of flame. Two tanks may not last a weekend.
Air makes a good insulator but an air mattress is constantly moving that air and is very cold to sleep on. Heated mattress is great. Insulated air mattress works well too there are foam filled version available.
Just like showering with a friend conserves energy sleeping with one keeps both warm. 30 pounds of Dachshunds, though, puts our more heat than a 120 pound human.
-- Chuck