I used Rustoleum on my SOF, I believe it was their "Professional" series or something with a similar name, I used the flat version over light weight polyester. Its ok as a skin coating, not particularly flexible (its got a lot of hairline cracks in it after a year - they don't leak, though), nor particularly abrasion resistant. I know some have had success with it, but I'm not sure if my experience stems from the light polyester fabric (too flexible?), a year of UV and weather exposure, or the coating itself. I've heard of at least one skin boat guru using it over Zar poly to repair and renew a couple of hulls, so that might be a better way to use it if you want an opaque skin.

Rustoleum's marine line looks promising, however. I'm going to use their spar varnish from the marine line on the kayak I'm building right now. Its tough and flexible, almost rubbery in feel, and the sample I made 5 months ago is still as flexible as it was a few days after I applied the coating. I'd wager their top side marine enamels are similarly flexible, but it always pays to make a test sample to be sure.

: Many people use brush-on Rustoleum, which is pretty much an oil-based paint.
: It was originally developed as a marine application to prevent rust on
: commercial fishing boats, and they do also make a marine coating, but
: their tech reps don't recommend using any of their products on fabric like
: a skin boat.