It's hard to say without seeing what you've got to work with. I had a old wagon ('84) that had some major rust around the rear. I did a quick fix for inspection (knew I would only keep if for another year or two) that involved riveting strip metal and using fiberglass and bondo, priming and painting over. It was actually damn secure and we were even able to bend it to reattach the rear flaps. Did not look hot, but then neither does large holes in your car. And in high-school you didn't need a hot car if you played soccer?