Pinhole Remedy After Welding Sheetmetal Patches?

I've done a few panel replacements in my time. If I get pinholes, I go back over with the mig. Fiberglass expands at a different rate than metal. Eventually it seperates. Remember the hoodscoops people glassed on back in the 70s, and 80s. They always cracked. When done, I use seam sealer.