Aircraft grade sheet metal is available in numerous thicknesses down to paper thin. If you uses an aircraft grade sheet metal you wouldn’t want to polish it. Most have a pure 1100 aluminum coating or ALCLAD that act as a corrosion barrier. But you wouldn’t want to have the aluminum in contact with the salt water. Any Compromise of the aluminum would lead straight to messy, flaky corrosion. I used to work on helicopters that hovered over salt water. The only solution would be to Plate it via anodizing or chemically and toxically plating which would give you a gold color.
It can be done as rasta shows. You can also laminate over the aluminum. Seen it done. Pre honeycomb aircraft structure often were sheet aluminum and fiberglass laminates… lots of em.
As for the Sun…
You wouldn't expose the deck when out of the water. I have a couple boards with black carbon full deck patches....
no problem in the water…
you would want to avoid heat at all costs witha foam core. That is why you rarely see a bare aluminu finished composite aircraft… you would want to paint. Poly at that…
don’t let naysayers here stop you from any project. The only way you’ll know for sure is to do it yourself as Molly aka Delbert Pumpernickel told me in person…