I just carry my Glock in a dry box if I carry a gun at all when boating around FL. I have a Remington 870 Marine Magnum, but that's for home defense and the Bahamas.
Protect yourself from the real threats which face boaters. The biggest ones are dehydration and exposure. Always have at least one or two sealed gallon jugs of water, some foul weather gear, some warm clothing in winter, and some way to get out of the sun.