This is what I use and it's pretty reliable. Large thin or flat items will warp a bit when heated but I don't generally have trouble.

Alumilite Amazing Clear Cast [0.5 gal A + 0.5 gal B(1 Gallon) 2 Part Liquid Kit] High-Gloss Plastic Finish | Multi-Purpose Epoxy Resin for Casting & Coating Countertop, Wood Crafts & Encapsulation Art https://www.amazon.com/dp/B087KPRJM5/ref=cm_sw_r_apan_i_ZSV5CAHB3C5PE6AJPY5K?_encoding=UTF8&psc=1