Off-grid, no ICE source will run long enough to get to full if lead, need shore power or solar for that.
So bank will not last long, go cheap, like
Duracell (actually Deka/East Penn) FLA deep cycle golf cart batteries, 2x6V, around $200 per 200+AH pair from BatteriesPlus or Sam's Club. Deka labeled same batts also sold at Lowes.
The AH usage per day of a mains fridge + inverter will be a lot more than a 12V compressor type like Engel, ARB, Dometic etc.