You should be laying up a total of like 1500 - 2000gsm of fabric, and using a ‘laminating’ epoxy resin such as this.
There’s a good thread on enclosure making here, but the quick rundown is:
- consider just doing the positive mold method instead of the positive-to-negative mold method since it’s easier to learn
- use plenty of release agent on the mold (PVA or wax, usually)
- set everything up you need before mixing epoxy
- brush epoxy underneath each layer so it soaks in from the bottom instead of brushing it on from the top
- consider using a cheapo vacuum bag system to get cleaner and more structurally sound results. You need at minimum, a 12v vac pump and some tube off of amazon, a plastic bag, butyl tape to seal it up, peel ply cloth, and paper towels for a breather layer. Check youtube for vacuum bag tutorials.