You got me curious about whether the drain plug should be always be in
place or not, so I looked it up in the VW manual and the Dometic
manual. Interesting that nothing was mentioned in the Dometic manual.
The camper manual only mentioned "To drain accumulated water due to
normal condensation, open the screw on the condensation drain pipe."
I would assume that in normal operation you should leave the plug in
place. I've always left mine open! Now I wonder what, if any,
performance difference there would be. It also said that the flue vent
must be kept uncovered at all times and only when you wash the camper
or when using an automatic car wash should it be covered. It makes
sense that it should be off during operation of the fridge, but why
would they say "at all times"?

Keith O