Yesterday, I called Norcold about frost/ice build up in our 7XR refrigerator (2018/2910D). It turns out there is a warranty repair for "sagging doors" and bad door seals - either of which (or both) can allow moist, humid air to enter the compartments (refrigerator and freezer) and hasten the buildup of ice on the fins. After confirming I had registered my warranty, they advised a door seal/door sag repair kit would be sent to my local RV shop for installation at no cost. They also mentioned that there's a heat cycle that occurs every 49 hrs of continuous use to melt any accumulated frost - water is accumulated in a molded plastic tray against the back of the refrigerator and drained through a rubber tube with a pin hole located in the capped end of a drain tube. I checked the drain tube for the water tray (access through the outdoor removable panel behind the refrigerator) to make sure it wasn't clogged up (it wasn't).
If you purchase a new unit, please take the time to go through the pounds of literature in the owner's bag you receive at pickup. There are at least 2 or 3 warranty registration cards that need to be filled out and mailed back to the mfr. It might save you some $$$!