Gary,
It is still just fine, no loss of adhesion, no blisters etc. It was painted in 2010, so it has had 5 full summers of sun and travels as a test. It may be just a little less reflective but that is hard to judge. I lightly pressure washed it this fall after returning home from summer travels and it came clean easily. There is no sign of oxidation from the paint causing any streaks like the gelcoat did and I do not expect that I would have to repaint it anytime soon from what I see. I still see no downside to the Rustoleum Topside/Deck paint for our roofs. Not sure about how it would work over another coating.
Later Ed