I will also recommend POR15. They sell a starter kit with a small amount that may or may not be enough for your repair. I would wire-wheel the damaged/rusted area around the hole with the sprayfoam in place. Try sanding/contouring the foam to match the firewall. POR15 the newly cleaned metal surrouding the hole and let it cure. Then I would lay 6 or 8oz fiberglass cloth (not mat) over the area overlapping the metal at least 1/2" on each side of the hole, and saturate with epoxy resin. I would go to West Marine, etc. and use West System resins. They are very high quality but not exactly cheap. It will make a much more permanent repair than duct tape.... I am local to you and more than happy to take a look at it if you are interested. RT

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