Additionally, in my experience, two-part paints are ill suited to application over wood. The expansion and contraction caused by varying moisture content can wreak havoc on two-part paint's hard consistency, leading to cracking, water migration and release. (To some extent, the same fate may befall enamel paint. However, it's far easier to repair and less expensive, and its life expectancy is admittedly shorter, making failure somewhat expected rather than a heartache and wallet-buster.)
Two-part paints fall squarely into the advanced DIY and professional category; not surprisingly, they cost more than single-part enamel paints. But based on their extended longevity, which could be a decade or more, the added expense can be amortized over time, ultimately making it more economical and the logical choice for painting fiberglass hulls and decks.