If you have MEK, that is the best epoxy thinner I've tried. Second on my list is acetone, and third is methanol if I'm in a pinch. I'd avoid any product that has water in it, such as rubbing alcohol. I know you can drive the water out, but why bother. Just get some MEK or acetone. Sometimes you can get MEK at hardware stores (my local Menards carries it with the paint thinners), if not try a auto paint store.

As for heat cure, depending on how it is done and depending upon the epoxy, it typically strengthens the epoxy. The heat encourages more bonds to form, resulting in a stronger structure. The heat MUST be applied during the cure and cannot be applied after the fact. A quick shot with a heat gun won't do it. You generally have to "bake" the epoxy at about 140F-150F for hours (I typically bake for 12+ hours) as it cures. But this doesn't really apply to epoxy as a fuel proofer and is more along the lines of making composite parts. I offer the tidbit only because the question of heat was brought up in a previous post. Cheers.