Epoxy or Polyester is just the resin system that the cloth was infused with. When you sand on it, polyester will have a strong smell, epoxy will not. There is a debate ( isn't there always ) whether you have to use the same resin system that the part was made from. IMO you can use epoxy to bond wood onto polyester parts just fine. Just remember that the bond is only as good as your prep. The surface must be scuffed and clean. Don't skimp on the clean, your part at this point may be oil contaminated. Wash with Dawn dish soap, scuff and wash again with Dawn. Adding fillers to the epoxy won't hurt but also don't add as much strength as some would like to believe. As Sensi has stated, the best way to make it bullet proof would be to add some cloth to the joint.