Rusted body

[Alchemist]

Surface corrosion or deeply pitted rust areas all need to be chemically treated. I would suggest you go to your local automotive paint supplier and inquire what they have available for you to use. You might consider speaking with someone at a shop that addresses alot of rust issues. There are so many treatments for rust so it would be to your advantage to make your inquiries and then make your decision.

Only after you've treated the rust concerns should you follow up as goatman said, to apply a good DTM (direct to metal) epoxy primer as your foundation prior to doing any filler work.

I would also suggest you acquire all the product tech sheets for any of the chemicals you plan on using to address your rust issues.

Good luck!