* BLUF: Bottom line up front
Assuming you have a good quality group 27 battery, expect about 100 amp hours apiece for a total of 200 amp hours without only 50% of that usable to extend battery lifespan.
for residential fridge power consumption, you are looking at 2,000 watts per day. At 12 volts assuming 100% efficiency of your inverter (really 85%), you will be using about 166 amp of battery per day.
Power from vehicle is neglible in that the wiring is too thin to support any real effect on battery charge and power delivery to battery.
In theory, if you have sufficient tow vehicle alternator residual capacity, then a a large wire (use a website to calculate necessary wire size for a given run and amperage) run from alternator output to camper battery should work just fine.