The fridge/freezer runs off the battery in the car, so as long as you do a certain amount of driving each day or two, the auxiliary battery will recharge as you drive and power the fridge.
Typically, a full battery (either car or trailer) can run the fridge for approximately 3 days without driving to recharge.
You do not need to stay at powered campsites every night! We would recommend staying at a powered site once every two weeks.
For more information on managing your power with a 4WD and Safari Camper Package
For more information on managing your power with a Safari camper trailer by itself