When I was a kid, my dad brought home a Starcraft pop-up camper with two propane tanks on it and we hauled it with a '69 Buick Skylark or a '70 Chevy Nova. Looking back on it, things would not have been any better or worse without propane for the little furnace, but once we upgraded to the new GMC Motorhome in '73, things may have been a lot worse had it been an all-electric vehicle, especially in the summer of that year in the Southwest where it was hot enough to be running both air conditioning units while driving through the desert. The fridge was always running, and at night we'd have the interior lights on as we went along. The 4-burner stove ran on propane and the water heater was electric. Granted that downtime at the campsite would have been the perfect opportunity to recharge, but now I'm talking about a 26-foot family-sized behemoth of the road that time. The body was a fiberglass shell and we had additional on-demand power coming from the gasoline-powered Oman generator housed in an exterior compartment. According to Dad, the Oldsmobile-made 455 CI engine in it averaged about 10 MPG, which was not too shabby for a 26-footer like that back then.
https://silodrome.com/history-gmc-motorhome