A lot depends on you and the way you camp. How long will the heater run during the night?
There is a sticky thread in the A-frame section that lists current draws of most stuff in an A-frame or PUP.
I did not want to deal with solar panels in Colorado winds. I also did not want to deal with the space, weight, and gas of a generator.
But I did want to dry camp for up to 4 days/nights, so I needed to figure how much battery capacity I would need. The heater fan is the big draw at 4 amps. So I assumed up to 5hrs run time, which gives 20AH per day. I set the thermostat to 56 on a cold night. A-frames are better insulated, and have about 1/3 the interior volume of a PUP, so the 5hrs is valid (for us) with night temps in the high 20s and day temps in the 40s (worst case). The CO/propane detector at 250 milliamps sucks another 6AH per day. We use flashlights more than we use interior LED lights. So our worst/best case is 26AH per day. More typical when heaters are used is 30-40AH per day from what I have seen posted.
Result for us is dual 6V golf cart batteries rated at 232AH each. This gives 116AH usable without recharging.
High wall units that have thermostatic control fridges have a DC control board that will add to the daily load.
2014 Rockwood A122 A-frame
2008 Hyundai Entourage minivan