On our last coach, we had the Norcold 1200 that would require de-frosting on most trips. I think most RV fridges have some sort of drain line that goes to the backside of the fridge terminating into a small collection cup. Taking off the vent panel, I noticed that the cup was dry and I thought that might allow warm/hot air(similar to a dry "P"trap) to flow back into the refrigerator via the tube. I put some water in the cup and made sure the end of the drain hose was submerged. I also added a small amount of veggie oil to cut down on evaporation.
The next two summers, we took trips that lasted 5 & 5 1/2 months without having to de-frost either the fridge cooling fins or freezer side during those trips of constant use. We also could lower the temp number due to the fridge side freezing food on the lower shelves. The freezer side still kept the ice cream solid.
This may not be all of your problems, but should help cut down on the 'frosting' and add to the efficiency of your(and maybe other's) fridge. We kept one of those small "D" cell fans on both sides to keep air circulating... that seemed to help too.