During warm weather, I put a few half gallon bottles that have been filled with water and frozen. (Fill the bottle to the top, squeeze tight and put the cap on while still compressed to give the ice room to expand.) I find that the fridge stays colder on the road and maintains a more even temperature when at camp. It also give me a way to drink ice water for a whole weekend.
It does take up a lot of space in the fridge, though. OTOH, if the fridge is already filled with cold things, the extra ice will not be as important in keeping an even temperature.
2012 Rockwood A122S
2008 Toyota Tundra Double Cab 4X4
Former owner of a 2002 Coleman Niagara GTE