MaShEdPOTaToEs said:
would it work if i applied tiny bits at a time?
Do you mean on the inside? If yes, then I'd say no. True fiberglass hardens about 10x harder than fiberglass bondo. Probably more actually.
You can flex the bondo to the point it cracks. You can't do the same with the fiberglass...unless you really try.
On the outside? Sure, but you're REALLY going to have a pita of a time sanding.
And you're not going to be able to put in the details you can with regular bondo.