If you are going to thin epoxy there are a couple of things you need to be aware of.

1. Rubbing/Isoprophyl alcohol contains water. Use DENATURED alcohol or acetone to thin.

2. Do not thin more than 10% BY VOLUME. More than 10% and you have a very high probability of the epoxy not curing properly (or curing at all ).

3. Heat (via a heat gun ) is your best bet for thinning the epoxy. It is safe and will thin the epoxy very nicely.

FWIW - I have read mixed reviews on using CA for fuel proofing. SOME people say that the nitro in the fuel will weaken/dissolve the CA. Water base polyurethane (MinWax Polycrylic ) is fuel RESISTANT, oil base polyurethane is fuel proof. If you do not want to use epoxy for fuel proofing, use clear FUEL PROOF DOPE (2 coats ) or Ultracote clear or Lustercrap clear.