Some people back east in Pa used Duck Tape as a temporary repair for their inspections. You could soder a piece of metal to your other metal parts. Then paint it. Make sure you remove the rust first. Other than that I suggest you do a web search for this type of repair. Then go to a repair (body) shop and ask them what they would do to fix the hole and the cost. If it’s too high ask them for any suggestions on repairing it your self. Sorry that I can’t offer a better suggestion than these.