polyurethane foam

I was wondering if i can fill in some of the stuff on my car with polyurethane foam. I was thinking about covering the top roof rack holes on the top of the car and filling in the door handles like this too. I was thinking i can lay in the expanding foam in the door handle hole, screwing it down (or is there another way), and then glassing over the foam, and finishing with some bondo if necessary. Can it be done?

You'll need to glass it. But I'd say just get out the welder and patch it.

yeah trying to shave stuff with fiberglass is not a great idea