ORIGINAL: FatBoy123
if maybe I should use resin and hardner (that comes with fiberglass, ofcourse without the fiberglass) insted of the normal 30 minute epoxy?
Use it for what? If it's a matter of mixing up 1/4 oz to glue in the firewall, then no, use the epoxy. If you're talking about using it to fuel proof the engine and tank compartments, or for fiberglassing the wing joint, then it will work fine, and save some money.
If you crash a lot, you might want to look at spad.org .