If it's structuraly ok but has pinholes I'd be ok with fiberglass. Of course new steel is always the ultimate. I have some pinholes in that area on my 55 and will use glass. My concern is distorting that area trying to weld patches and not having the glass and seal fit properly afterwards. I've welded new metal on all other places on the truck. I'll also use the fibergalss(ground glass and resin)over all welded patches to waterproof the patch. There are always pinholes and you can do more damage trying weld every last pinhole than it's worth.
Good luck,
Keith
