We do a fair amount of dry camping, and have a lake lot, currently with no electricity.
Two seasons ago, I upgraded to 2) 6 volt GC2 golf cart type batteries. They are rated at 105aH each, in series gives me 210aH. That is about triple what a typical stock house battery is.
They are available from Costco at under $100 each.
I even got a nice battery box that fits like it is made for the original space behind the LP tanks.
I can get three days use with no backup, with the furnace coming on a few times during the night. I sometimes leave the camper at the lot with only the refrigerator and other parasitic draws running, and have gone 5 days with batteries discharged to 65%.I don't discharge past 50%.
I have added a 200 watt solar suitcase, and can now go as long as needed, if i can get full sun for several (6 or 8) hours.
Otherwise, I run my generator a few hours to keep them charged if needed.
Doug and Patience and Shelby the mutt
2015 Crossroads Sunset Trail Reserve ST26RB
2013 Ford F-150 3.5 EcoBoost XLT Supercab 4x4