When I have my RV out dry camping on weekends, what I do is use a number of hard-sided ice packs and a cooler. At the S&B house, I keep a few large ice packs in the freezer. Come Friday, I toss my food items and the packs in a cooler. When I hit the RV, I flip the fridge on, put two ice packs in the freezer and two in the fridge, then turn the small fan on inside the fridge part. In about four hours, the ice packs in the freezer will end up refreezing, so I swap the fridge and freezer packs. From there, the fridge can do its job until I am ready to leave, and repack all unused food and ice packs in the cooler and turn off the fridge.
If I had the ability, I'd just leave the fridge on for convenience sake, although I'd leave some ice packs in the freezer and fridge so when I turn the fridge off for a trip, stuff stays cold longer.