The cats we've been on, have a recess below the bottom rack that allow us to put a bag of "beverage ice" at the bottom of the fridge. It's on top of one of the two cold plates and always stays frozen (fridge only has one cold plate).

Haven't had defrosting problems at all, in fact with a generator we run the fridge and freezer at night, but turn it off during the day; or at least while underway. This helps preserve some of the vegetables that wilt/freeze easily.