Laid up my 42' sloop
periodically for several months over a total of 11 years in the Eastern Caribbean
. Never had a mold
problem. Boat has 3 cowl vents and vented louvered main hatch
Air circulation is the key. And, it's a misconception that just because boats are in the water
is necessarily damp. That's just not so. I found in 17 years as a liveaboard
that dampness was rarely if ever a problem, though dryness was.