+1 on JB weld (epoxy great for metal bonding). Use it with two pieces of sheet metal. One to plug the hole, and another to back the plug and overlap to the CPO. Basically a patch with the plug to fill the hole to a flush surface. Welding is great, but heat control is crazy important to prevent warping. This method will obviously nix that worry. Using layers of fiberglass is excess work, hazard, ugly as fuck, and is not necessary if you use JB weld and metal peices.
I had a CP taco on me because the clasp anchor acted as a heat sink and caused uneven heat distribution leading to a taco shaped warp. Luckily a buddy has body repair tools and slapped the warp out of it... Still actually taco'd a little, but when installed it sits perfectly flat.