Before our current rig, we would defrost twice on a 8 to 10-week trip. Our current refrigerator is (almost) frost free in the non-freezer compartment. Now we only defrost the freezer once on a long trip. Of course, usage and environment plays a role. As the manual says, "Defrost as needed."
We place the frozen food in the sinks and cover with towels.
We place bowls of warm water in the two freezer compartments. The manual will warn you not to use hot water or a hair dryer - Most of the time, we do use a hair dryer on cool - heating element off.
Make sure the drain for the water catch tray under the fins is working properly. Ours has a plug on the outside that is used to keep bugs from entering, while in storage.
How long? Not really sure We do it in the evening, while watching a movie. And we're finished by the time the movie is over.
Tom
2015 Meridian 36M
2006 CR-V toad
3 golden retrievers (Breeze, Jinks, Razz)
1 border collie (Boogie)