Space was too valuable in our truck camper so we didn't buy even a small generator for our 8-week trip. The biggest use of camper battery power was the furnace fan in the morning and maybe the water pump.
During our 3 nights at Teklanika in Denali NP, we just idled the truck engine for 30 minutes during the allowed times and we were charged back up. I don't usually idle the diesel for that long but made the exception there.
Driving around a bit after boondocking also did the trick.
Our trip journal. 2014.