My tow vehicle has a 170 amp alternator so I have no concerns about draining the battery. On DC, the current draw is 10-12 amps, so you won't want to run it too long once on site. I added a fridge fan to ours. See:
The batteries are a bugger to install but last a long time. On ac with the fan running our Fridge's temperature is 40 degrees with the thermostat set on 5. We switch the fan off and store it when traveling. Once on site we switch it on and place it at center rear prior to loading the fridge.