We have the 12v fridge you're describing with a 480 AH bank (4×120) and it's been a minimal draw. We have yet had to manage battery usage beyond what we previously were used to with 480 AH AGM (4×120 series/parallel).
The fridge has a night/sleep mode, and has performed flawlessly. I had a 2014 Mammoth with the standard 2-way Dometic that had issues probably due to not enough ventilation and possibly too much un-levelness. I opened the camper side door and found greenish coolant puked out on the vinyl floor. Coincidence the back window is big enough to throw an old fridge thru?
