You can repair it with Bondo in the same way that you fix automotive fiberglass bodies. Because both the car body and the door skin are going to move around in use, there will always be a question about how long the repair will hold up. One other issue is that when you stain, put another coat of paint over the fiberglass. This will hide the color difference between the paint base that’s on the door now and the Bondo.
You use a gel-type stain on fiberglass or metal surfaces and the paint department of your home center should have the instructions and tools for doing this job.
Personally, I would take a long look at the cost of the door and the finishing materials before doing the repair. The repair could last a lifetime or could fall out the first time the wind grabs the door and bangs it or someone slams the door.
Henry in MI
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