Condensation on boats can be largely due to all the moisture exhaled whilst breathing. Two quite simple solutions for this are as follows.
Snorkels. These can be got with extra long tubes which by punching holes in strategically placed positions in your roof say above your favorite chairs and bed for the snorkel tubes to be poked through. You can then stick the instrument's mouthpiece in yer gob and exhale to the outside to you're heart's content all that breathy moisture.
The second method is more simple, but requires some electrical power and makes a rotten noise. The wet'n'dry vacuum cleaner of ''Henry'' fame will if a flexible sucking tube nozzle is chosen carefully that suits your lips embouchure will happily suck all the steamy breath out of you. I would advise wearing ear muffs with this method though.
Hope this helps.