Up to a sunny humid day approaching 100*, our 12-year-old Norcold will maintain acceptable temps, like 40 and +1. We make sure the doors are firmly closed, and I added a couple small computer muffin fans to help air circulation up through the coils. The fridge doors benefit from the A/C inside the coach, but the fridge itself (cabinet and coils) are essentially outside.
What has to be avoided is the behavior I call "Shopping" where somebody stands with the door open trying to figure out either what they want or where it is. You know, like at the supermarket, propping the pizza freezer door open while reading a dozen labels...
