[bobss396]

I go with jcat's recommendations. I have used aluminum flashing with pop rivets and or sheet metal screws. The aluminum forms easier to contours and you're really only buying some time. I used liquid driveway sealer around the edges and it kept the interior dry. I went under and squirted gutter and lap caulk from the bottom too. Some places are hard to reach, like around the transmission cross member.

Another alternative is to use fiberglass. You cut out all the rust, grind down around the edges to bare metal, mix up the resin, coat the edges and lay down the cloth. Let that set up and then coat the fiberglass with the resin. This method is best for smaller holes, not good for big expanses of missing metal. It can be combined with the metal patch method and use strips for the edges and seams.

Bob