[Superman]

Sure sounds possible. Maybe I'm missing something. Most if not all the above suggestions are excellent. What's so hard about drilling through both pieces and driving an interference-fit pin in there? Or as Tim says, open a couple of little ports in the sheet metal, and weld there. If the engine and exhaust will need to come out eventually, then you lose nothing with the gamble. Worst case scenario: The sheet metal gets a bit warped.