I can tell you first hand that the marine environment is quite harsh on music gear - ALL MUSIC GEAR! The salt air tried to eat my arranger keyboard stand, my Quick-Loc folding stool, and everything else. I performed in the Florida Keys and all along the eastern seaboard using my Yamaha arranger keyboard, it continues to function perfectly, despite the horrendous conditions of extremely high humidity.
Now, I performed with a couple guitar players, one of which used a carbon fiber acoustic guitar that sounded incredible. He added a pickup, one that fit in the opening and was held in place with spring pressure. It never went out of tune, and the entire time he had it aboard his boat it never saw the inside of a case. I know it was not a low end guitar, but I cannot remember the brand name.