Aleš Lombergar

Yes it will, however I recommend that you use a wire brush and clean all the rust off first. I have used fiberglass to patch metal pipe which was under about 150 psi and have had it hold a long time.

Yes, fiberglass will stick to just about anything. The fiberglass actually comes in a fiber weave that looks like white cloth. You then saturate it and the installation site with resin that hardens. The fiberglass is really just a lattice structure to provide strength to the hardened resign. I wouldn’t recommend application directly over rust if you can help it. Grind, sand and or sand blast away as much of the rust as you can and then use a chemical rust converter that will de-oxidize any remaining rust. Clean that up and then apply the fiberglass and resin. Let that fully cure. If the holes are very large, more than a couple of inches, I recomend backing the holes with sheetmetal prior to application of the fiberglass. I would then spray the underbody with an undercoat sealer which will both hide work and protect the interior from water penatration in the future. The inside can be painted with something like rust-oleam spray paint and then covered with padding and carpet. If the rust is pervasive, it would be better to cut out the whole floor pan and weld in a new one, costs a few bucks, but it will last longer.