To answer your question, when we overnight in a parking lot/rest area, we make it till the next morning on the 2 built in batteries, IF we don't run the heater too much (if it's not too cold). If it's fairly cold, i'll set out the genny.
We boondocked near wolf creek pass and silver jack res. in Colo this past july.
2018 365 BH w/res fridge.
in addition to the 2 - 100 amp hour batteries in the 5er, I built a sort of external power bank: 4 100 amp hour batteries (free to me) in an external box in the pickup bed, with a 3000 watt inverter ($369), 80 amp Prog. dynmics converter/charger ($269). and we have a 3600 watt gas/prop genny to recharge the batteries a couple times a day. I'd say we recharged maybe a total of 3 hours a day?
I plugged into this set up just as with shore power, but turned off the inboard charger when not on the genny.
This set up worked well for the two weeks in 45-80 degree temps.
We were above 9000' most of the trip so we never turned on AC
Ran Coffee maker, Microwave, TV's, dish etc as we would have if on true shore power.