Not being much of a body man I purchased 2 lower rear corner patch panels for my 57 3100 abd went ahead and cut out the exact size of the patch minus about one inch. I removed the old skin only to find an inner panel. This inner panel seems to be part of the floor pan. Is it? I have read where some kids just fab their own piece of inner panel if you're not building a show truck. I have not found inner patch panels anywhere or else I would just buy them and weld them in too. Anyone know?