I've been using automotive urethane as a clear coat. I've sprayed it over Krylon brand paint, Hobby Lobby acrylic craft paints and over automotive basecoats without issue. It is fuel proof and easy to apply though you should use a good respirator to protect yourself. In fact with any of the two part paints a respirator should be used. The urethane I've been using is just a "house brand", Autobody Master brand. I've been happy with it. It sprays nicely and has good gloss without any extra work. It could be wet sanded and buffed for additional gloss if you want to.
Ken