I have my camper rigged to run on 12v. I have a plug in if I want to plug into shore power and it will power my battery charger and an electric heater. Same plug can plug into a genny. Everything in my cargo trailer runs on 12v. So if I have no power, 2 12v batteries this year never drained down for 2 weeks powering only led lights & water pump. I crack a window and use a buddy heater connected to a propane tank outside. That same propane port heats my on demand water heater. Alway crack a window if you are using a gas heater. And install a CO alarm. I installed a bathroom sink, toilet and shower, 60gal water holding tank, full size bunk beds, exhaust fan in the bathroom and a super exhaust fan in the general area that will suck air through the open windows and feel like AC at night, but the fans draw a lot of watts and I don’t use them unless I can charge my batteries.
Some pics are older. I’ve been updating through the years.