The BF or NL construction does not trap moisture in the walls any different than other construction methods. Any construction method that is so lose as to let the moisture out, will let plenty in. The inside of a BF or NL is just as "breathable" as other methods.
Production boats are almost all built with a joint at the deck/hull, and these are notorious for leaking. Boats also have numerous deck penetrations for hatches, hardware and rigging - more even than an RV - but they are sealed much differently than a typical RV. Not without problems, but no where near the problems that RVs seem to have. In this respect, a BF or NL can be sealed like boat deck hardware, to the extent the particular piece of hardware allows. The factories do not do it unfortunately, you have to do it yourself.
