You do NOT need any caulk around the fins at all. ANY gap you see, is normal, IF the CU was installed correctly. The Thermal mastic is between the Fins and the cooling unit and IF DONE correctly, you will not see any of this on the fin side. There are NOT operational problems with the 1200 series Norcold. They have made millions of them and the only problems are problems due to AGE and normal wearing out of components. If FIXED correctly, they perform great. Doug
From your pics, The freezer, that gap is normal and the FOAM insulation of the box seals that area
The fin with your sealant, also normal
Your model has an auto defrost feature. IF left ON continuously, every 48 to 54 hours the refer shuts OFF for about 2 hours to allow any frost/ice on the fins to melt. Then the refer restarts. FROST/ICE on the fins means that the refer is performing to specs. The inside temp of the refer will be 10 degrees warmer than the fins. If the fins are at 28 degrees, the refer will be about 38 degrees. I notice you had plastic bags and such in the lower refer. Those are a bad thing IF they are at the back wall. You need to have an air space of at least 1 inch at the back wall of the lower refer to allow air to flow up and over the fins to transmit cold to the air. IF partially or fully blocked, then the refer cannot adequately cool the interior items. That is why some install the refer aftermarket battery operated cooling fans to help move that air.