I just today shot four coats of medium-wet single stage automotive urethane on a section of my hood. The rustoleum is roughly a year old and has been sitting outside for a year. There were no adverse reactions between the urethane and the oil-enamel. I will post a comparison picture of the unbuffed urethane and the buffed rustoleum if anyone is interested but it is kindof a sad comparison. All I can say is that rustoleum black is not black at all but is more of a gray.