I've painted two sets of running boards with black rattle-can and I can tell you that it holds up pretty well. I put at least two coats and 3 if I could. Also, I went with satin instead of high gloss. My '50 is still pretty original and I didn't want the running boards to look new. Whenever I get a significant scratch I simply shoot a new coat over it and it looks good again, but I don't have to do that very often.
Don't be afraid of high quality rattle can paint. It's good stuff and no, you won't regret using it.
