Have you looked into mar-hyde Black Satin Automotive Trim Coating?
I'll be honest, this is the best stuff I've worked with. It goes on super smooth (you don't even have to be a good painter to good great results ). Plus it dries to a gorgeous satin finish that will keep on lasting. It's a little expensive but it is by far better than rustoleum and looks better than duplicolor IMO. I bought it at my local car parts store.