I painted the entire undercarriage / chassis of my '56 Coupe De'ville with Rust-Oleum semi gloss black 20 years ago. That car is my primary vehicle and has over 100,000 miles on it since then. The paint still looks the way it did when I put it on. I'll take some pictures today if you want.
I also painted a set of (iron? steel?) pool furniture with Rust-Oleum 15 years ago. It sits outside all the time and is never covered. It too, is bright and shiny and not faded, peeling off or rusting through.
