There is no such thing as a frost free RV fridge the last time I checked. Frost is just part of the lifestyle.
There are ways to avoid some of it. One is using a 12V fan on the fins. Best for the short term RV'ers not so much for FT/PT'ers. Other option is not to open it so much and look inside for so long. Last is what we would do. Which was a defrost every month or two.
I would turn the fridge off on a day we would be on the road. By the time we got to the park things were cool but not cold. Take everything out and into a cloth Walmart Freezer bag. Defrost, reload, good to go for a another couple of months.