Be careful when painting the top. If the paint is too thick or soft, you'll catch your edges on the paint itself... I'd say it's better to not paint the very top at all. You're just going to grind it off anyway. If you're worried about rust, don't. If you're using the rail enough, your skis will keep grinding the rust off before it becomes a problem. However, paint on the sides would be good cause your skis don't really touch there.