Didn't have fiberglass on my panel but have been running fiberglass fenders, both front and rear, as well as fiberglass running boards on my 37 Pickup for over 20 years. No problems and most folks tap them and think they are metal.
My fenders were made "hand lappiong" fiberglass and I feel they are much better than the ones made by spraying. Spraying is not consistent and will have light spots. .........all this is just my .02 cent.
....and I might add, be sure to keep any fiberglass fenders laying "flat" so they do not "set" and this is especially true with fenders that are "green" or still "fresh".
Got my fiberglass from Richard Keller, R&R Fiberglass in Tenn......he's been doing it for many years.
