As the original poster concluded, the problem was heat and humidity.
We have a DM2652 in our Class C Sunseeker. We have made several trips of several months at a time. I usually have to defrost our refrigerator during a long trip. We didn't have a problem during the months we were in the southwest.
Defrosting during a trip isn't hard. Since we have plenty of storage in our 3100, I carry an ice chest. It was handy on our first long trip when my dearly beloved didn't realize how small the refrigerator is compared to the one at home, and bought more groceries than we could have put in two of these RV refrigerators. When the cooler is in the storage compartment, I fill it with paper towels, etc., so the space is not lost. To defrost the refrigerator, I use a hair dryer, held well away from the refrigerator so the heat isn't directly on the plastic parts. It takes about 30 minutes, so the food is just fine in an ice chest.
You can get rid of some of the ice on refrigerator compartment fins if you shut it off sometimes while you are driving. The refrigerator compartment is usually about 40 F, which will melt the ice off the fins if the fins aren't being cooled.