Fiberglass resin is about 15.00 dollars bondo is about 12.00 and the epoxy clay is about 30.00 after shipping.
The fiberglass resin will make the pepakura piece sturdy and strengthin the item. Once it dries you can use fiberglass mesh inside with resin to give it a very strong and durable finish. This will make the bondo process easier and also protect your piece from collapsing or breaking. You will have to sand the bondo as it dries very fast when applied.