you could get epoxy resin + partb gardner from a fiberglass supply (i use it for boats), thin it with acetone a bit it will penetrate pretty well...that what i do when i'm going to use some plywood for core material. But will probably only come in a gallon. I get a gallon of laminating epoxy+hardner for $75 so keep that in mind depending on how much you need. That would surely keep it together...the stuff sticks like no other. for extra insurance glass a thin cloth layer 4 or 6 oz maybe? to keep it together too. Good thing with the epoxy is long shelf life you can use it for a long time for other stuff. Mix talc or cabosil,etc for glue, mix it thicker for filling. mix micro glass bubbles for fairing. Not sure how much of that applies to cars, i use it on boats.
