I'd start with heated leather seats. They'd not only look cool, they'd be functional in keeping you dry.
Next, I'd put in an electric spray skirt, kind of like a convertible top. I have one on my Mustang, why not on a kayak?
Looks like you have the custom paint job figured out. I'd consider those paints that change color based on temperature though. use the chrome as an accent.
For the body, maybe you could put some sort of a spoiler on back (a whale tail on a kayak - what a statement that would be!).
Put a kick-ass subwoofer in the back (balance it with some amps in the front), and a GPS system up front on the deck.
Good luck, and make sure to post those pictures when you are done!