Would I have been better off not knowing?

I can always try the MIG and if it turns out bad, it's not a big deal from there to cut out the area and weld in a new spare tire pan
...Yes that is correct.....Nothing to lose but your time....But I'm telling you , use a copper spoon on the back and little heat on the mig......You can build up those pin holes in the trunk pan and grind smooth with a great result that will be solid.....If not cut out and replace with new metal patch...nothing to lose man, but a little time....