What we did: Our A-frame was bought for long weekend camping in Colorado. We wanted to be able to go for up to 4 nights anytime snow wasn't an issue.
Based on past experience with a PUP dry camping at Lake Tahoe, we knew battery was the 1st thing to run out, and the most difficult to get more of while out camping. So I went for a dual battery install right from the beginning. Calculations were enough battery to run the heater with the thermostat at 55 degrees for 5 hrs/night for the 4 nights without taking the batteries below 50%. We like to camp in the trees pointed whatever way suits us. And winds are a problem for portable solar panels (and awnings) in Colorado. I did not want to bother with lugging and monitoring and fueling and storing and paying for a generator.
Actually, the calcs were conservative. The A-frames hold heat (or cool) a lot better than the canvas walls of a PUP. And there's far less volume to heat or cool. So I am quite comfortable with nights down into the high 20s. Below that, I might start worrying about the water tank freezing.
Due to a number of SPUTs (Stupid Pop-Up Trick) on my part, the two batteries were destroyed in about 15 months. In looking for replacements, I came across 6V golf cart batteries at Costco. These were Interstate batteries, GC-2 232AH, for $150 for two, including tax. I measured carefully - they fit my battery box better than the two size 24 12V (which cost $85 each). So I now have more battery capacity, and for less cost (see pics below).
I installed a battery cut-off switch on the end of the battery box. The wood battery box cover I made because the plastic one disappeared in the winds while driving down the Interstate in Eastern Colorado. One strap is not enough! I now use two bungy cords hooked on eyes in the cover. The last pic also shows the remote for my fridge thermometer. I use a standard Walmart wireless thermometer (less than $10) to monitor my fridge temp while camping.
I am a happy camper.
2014 Rockwood A122 A-frame
2008 Hyundai Entourage minivan