Just mix up some 2 hour epoxy. its almost like corn syrup mixed with water already... no need to thin it. Heating will thin it a bit, and will sped the cureing.

2 hour epoxy generally takes overnight (up to 2 days!) for the surface to quit being tacky. Don't worry about it.

I advise against thinning epoxy with alcohol. You can make the epoxy "spongey" It can feel almost like rubber and be porous enough that its worthless for fuelproofing. Its too easy to do it wrong. Use 2 hour epoxy instead.