Hey, bigbird;
Here is a picture of my air tank install. My Cat is a CMP not a knock off. I bought mine from AKModels and Alex convinced me that the CMP version is worth the extra money. But even though yours being the knock off, I don't believe the would have used polyester instead of epoxy. The reason for my assumption is simply, you have to be extremly quick to lay up the glass work in such a confined space like a fuselage mold. Polyester is normally used for boat hulls and the glass/polyester resin sprayed in. Polyester sets very fast. You have to work quickly and with no interruptions. That doesn't work for small, delicate jobs like a fuselage. So I believe you still have a regular epoxy/fiberglass fuse, like we all have. Just rough up the areas where you wnat to glue and use 30 min epoxy for your glue joints.