First-time body repair on my 16-YO DD... seriously doubt I'm buying a welder and taking a welding class for this (although it would be cool to know how!).

What I have in mind at this time is to grind away the rot to clean metal, and use some type of metal-reinforced filler product after treating the exposed metal to try to keep the rust from returning.

Does this fall under your "Basic Backyard Bondo" job?