When I bought my 16 foot Dura Craft, someone had painted it with the wrong type of bottom paint. As a result of the electrolysis, the bottom had some pitting, and the center keel was completely gone.
After I sandblasted all the old copper paint off the bottom, and got to bare metal, I re-built the center keel with a piece of aluminum angle. Then I painted the bottom with the 2 part Rust-o-Leum truck bed liner. Going on 7 years later, and well over a thousand hours of use in salt water, it's holding up pretty good.
My only suggestion would be to prime bare aluminum with zinc chromate primer, to give better adhesion of the coating.