I just patched a rust thru in the drivers side floor board and used a piece of 18 ga. galvanized sheet metal. I have a sheet metal break that I was able to use to match the floor board stiffening corrugation pattern. After cutting out the rusty parts, I fit the piece to overlap about 1", turned down the edge at the transmission hump for stiffness, put caulking on the laps and bolted thru the lap with 1/4" machiine bolts. With the floor mat installed, you cannot tell the patch is there and it is very solid.
no you should weld in new peices of sheet metal replace the whole floor w/ new on or. pop rivit the holes closed. It really depends on how large the holes are. Myself, my drives side was the seat bracket was rusted so bad that it fell through the floor. the transmission hum was also bad. So I cut out the bad rust area and welded in a 3/16" peice of sheet metal over the rusted holes.
If you are considering Bondo then I assume that your talking pin holes.
They, of course, represent even more rust damage that you can't see. I cut my panels out and flange welded in some 18ga. If you wanna just fill some small holes in, POR sells a two part putty that dries super hard and is good for this.
Bondo sux, it will attract even more moisture. I would only use it to fill SLIGHT imperfections where the back side is not exposed. Fiberglass cloth works well if you can't replace the metal.
The holes are round drilled holes averaging 1/2 inch that where drilled for various reasons throughout the years. They are not rust holes. My dad said I could put bolts in the holes. I gues thats a quick temp fix but I wanted to make the holes disapear. I don't weld so I guess I will have it done. Or try that POR product. Thanks.
There is a hardware store paste called "DevCon metal patch and fill", that I have used to fill small screw holes like you describe. I have been very happy with its adhesive properties, and it can be sanded down and painted so you don't see the holes at all. You can build it up in layers for the bigger holes, but I think you would find the 1/2 inch and larger holes challenging.