Classic/Antique Car Repair: rust repair, minor surface rust, rust killer

Question
I would like to know if you have any previous experience with rust repair/prevention?  I am restoring a 1969 Ford Mustang.  I will be replacing several outer sheetmetal pieces, but what about  minor surface rust on the underbody, firewall, etc?  I can grind off the majority of the rust, but how do I keep it from returning?  Have you ever used any of the "rust killer" products on the market; like POR-15, Zero-Rust, etc.?  Any info would be appreciated.

Answer
I personally have no experience in this area - I  have always had professional help with my body and paint work, except for minor repairs.   However, the scuttlebutt in the industry is that POR-15 and Corroless are both very good in stopping rust.  They may not be easy to get a good looking finish over, however, so best to do a test panel to see if you are happy with the result.

I live in the desert southwest, so we don't see rust out here - no chance to learn much about it!

Dick