If I were the one repairing the rust, I'd cut out the rusted section and weld in a new section. Depending on whether or not a factory panel was available, I might have to fabricate a patch panel, using the same gauge metal and fitting it carefully for minimal gaps. My next steps would be to weld it in, clean the metal thoroughly, spray both sides with an epoxy primer, and then color coat. That's the simplified version, of course, and there are some weld nuts that would need to be added for the bracket, but that would be the basic plan. As a side note, automotive steel is a high-strength steel, so (with no insult intended) Home Depot sheet metal is not the best choice.