Hi, there are are lots of good ideas above but the best one is to seal as many holes as possible. You can fiberglass(clean back to bare medal), make patch panels and use marine sealer and pop rivets(or sheet metal screws) to hold in place,on the under side spray on undercoating, top side paint.DO it under the size of the replacement parts. If it is a bunch of pin holes see about getting bed liner sprayed on the floor and firewall.
