[JimD]

Happens on pretty much all vehicles. The zinc plated bolts linked above may work. The principal is the zinc is a sacrificial material that oxidizes readily preventing oxidation of the steel. It works as long as it stays intact. If you scratch if off, the steel can still rust.

Common "stainless steel" is 304 which will rust, just much more slowly than carbon steel. If you really want hardware that unlikely to rust, you could use 316. If has much more chrome in it and is thus much more rust resistant. McMaster Carr probably has them. Their website is a little quirky but they give good service.