Lots of good suggestions, solar would be a longs term solution but not something you want to get into on the spot - we love ours
IMHO, the best approach would be to buy 1 (better 2) true deep cycle batteries and make sure all your batteries are completely charged before you leave and bee very conservative with your power usage, incl. fridge - also don't use old and new or different type/size batteries simultaneously.
Maybe ask the campground host if they let you charge batteries at their office or shop - you never know.
And start planing for a solar setup down the road.
2013 RAM 3500 Dually Longhorn
2014 Trilogy 3650RL, W/D, Onan 5500, 8000# Axles, IS, 960 Watt Solar, 6x6 Volt Battery Bank, Freedom SW 3012 Inv/Charger