I try to keep my crew from "shopping," spending lots of time with the door open.
We have a Norcold, and if there's good news about Norcold... It has a "defrost" every couple dozen hours. It isn't a forced defrost like a home fridge. Rather, it stops the cooling unit for half an hour or so, and the frost/ice usually melts in that time.
One of the many not-so-good things about Norcold... Our fridge door is so flimsy that the door gasket doesn't seal at the corner below the latch. We now have the Norcold Knee Knock and High Five. Nudge the bottom of the Fridge door and the top of the Freezer door every time we close them. Its now second nature and really helps with cooling and frost. Along with No Shopping...
Dometic doesn't have the defrost cycle. Luckily, Dometic DOES seem to have stiffer doors...
I keep a squeeze bottle with a Stream setting on board. On long summer trips I keep a air-pressured garden sprayer. If the fins get heavily frosted. I fill the sprayer with hot water, open the door and blast away at the ice with the fine jet of hot water. Ice is all gone in less than a minute of Shopping.