When I installed my Furrion backup-observation camera on the back of 5er I had to remove the plastic dummy look-alike first. The sides of my camper are fiberglass too. I had previously purchased a Bondo Fiberglass repair kit for a deep scratch I put on the front cap of the 5er. I used it to fill the holes for the camera, let it dry hard and then simply screwed the same screws right back in the same existing holes, except these were rock solid now. The screws snugged back down nice and tight.
You can get it at WallMart, Home Depot, any number of places:
Click here. Keep the rest on hand for other "hits" your fiberglass may take. It dries clear. And considering you are just filling a screw hole, it will take just a tiny bit. You don't need to use that mesh material for something like a screw hole. Be warned though, once it turns hard (after a few minutes) its HARD! You'll never remove it. So if you are sloppy with it, you'll have slop on the side of your camper forever. But it works great!
