Sub Enclosure Help

So I decided to fab up my own fiberglass enclosure over the weekend. Long story short, it turned out great, besides some air bubbles that I didn't get out. Since I really don't want to keep adding more layers of fiber, is it possible to use duraglass or some other fibrous bondo material and line the inside to build up some strength, or would it be too brittle to use?

Thanks y'all

 

I don’t know much about fiberglass, but you want the enclosure to be pretty strong so you don’t have issues later with air escaping if the box were to break

 

Yeah thats my problem, most of my box is fairly thick, but I have duraglass laying around the garage somewhere and would like to use that to thicken up the enclosure and add some extra strength, if that works