Ouch. What does the rest of the truck look like?
Get some sheet metal, pound it out to fit your floor. Go to Home Depot and get some Vulkem (good calk). While you're there pick up a pop rivit gun and a drill bit to match.
Calk the crap out of the floor, drill some holes for the sheet metal, pop down some rivits, put the carpet back over it and enjoy.
Should be able to do it all for about $25.
Then in the spring do it the right way, if the truck is worth it.
Good luck.