We have a late model Airstream, ours has the full metal interior and we have not had any moisture problems (other than the skylite leaking). Just like Grim Reaper said, once the heater is on all is good but using the vent in the bathroom and the stove vent is a must. When showering we have the vent runnind but in general we just leave it open to give a bit of circulation.
We have had ours down to 10 degrees and not had problems with moisture or freezing.
You don't inherit the world from your parents, you borrow it from your children.
1979 Unimog 416 Expedition Camper
1974 Unimog 421
2004 Dodge Ram 2500, 4x4, Double Cab, Cummins Turbo Diesel
2006 25' Airstream International CCD
2009 Harley Davidson
Sugarloaf, Boulder, CO