What others have said about the gaskets. We purchased our trailer in 07 and noticed a lot of frost in the freezer. NorCold reefer, upper freezer. The gaskets were all okay but I noticed a type of thick white plastic tape? on the corners of the freezer compartment, opposite the hinge side. This plastic tape was covering small holes used when the door hinges would be reversed to have the door open the other way. I removed the thick tape and used a very thin tape to cover the holes and the frosting problem went away. It takes very little to break the seal and have air leakage causing frosting. Hope this helps, good luck.