Sold a fellow boater who lives full time on his my Fender Acoustic with a very nice hard case. He opened up the case to play one day and the whole top of the guitar body and neck were wet. He moved it out to storage and brings it down to play. Shame.
I bring my Takamine acoustic down to the boat, but take it home, after hearing of the above.
I had a small electric travel guitar that I kept on the boat full time last year. It fared well for months, until one day I noticed the bridge starting to pop out of the body. Still need to fix her and bring her back down.
I would be willing to try out moisture prevention devices and media for the acoustic.
I do some of my best picking on the boat.