Body experts. Advice?

If I use RustMort, it's after welding I assume? Thanks for the help!

I would use RustMort before welding. It is really hard to clean up all areas before welding to bright shiny metal. After the metal is prepped, go ahead and use weld through primer where you ar going to weld epoxy primer everywhere else. Here is a picture of my 71 Barracuda floor board that had quite a bit of surface rust that was prepped with RustMort. After wiping it down to remove the residue, it was ready to prime over.

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