I spent a few hours today using 'De-Oxy-Does-It' to try and remove some rust under my battery. I removed a pretty good bit, but I still think I need to treat it with some rust converter. What would be the best thing to coat it with after that to prevent more rust? I'm thinking there should be a plastic battery tray under there, but I don't have one. This is the only area of my car that is rusty.

 

POR-15 to encapsulate the rust (they have a sample kit that would easily cover that area). The rubberized bed liner would probably protect it from future acid damage.

 

I ended up using the Permatex rust converter from NAPA. It worked fairly well, the rust turned black and now it has a hard coating. I'll look for some of the bedliner type stuff, if I can't find that I'll just have to settle for gloss black Rustoleum.