Many, many years ago I did a pair of amps with purposely rusted end bells and channel frames, a verdigris looking chassis panel and green flocking on the exposed transformer coils. Sorry I don't seem to have a picture handy, maybe someone else has a pic of it. People did seem to like it. I used some kind of chemical rust finish kit from Michaels IIRC. These days I would just take the end bell with me to Bonneville...Do cover the rust with a clear coat so it doesn't get rubbed off on your hands when you handle the amp.