I have to go along with RCKen and piper chuck, I've seen to many messes made by people thining epoxy with alcohol, some so bad the item was not salvagable.

The Krylon may or may not be fuelproof. Some paints were at one time and aren't now. Or weren't at one time and are now. So don't expect any paint to be fuel proof unless it says it is on the label.

If you plan to paint the entire airplane, use model airplane paint to be absolutely sure.

That said, polyurethanes are mildly fuel proof AFTER they've cured completely. That takes way more time than most modelers care to wait.

Which brings the advice back to: use model airplane paint for painting.

If you figure to fuelproof the firewall of any model, fuelproof paint works to fuel proof. If you wish to strengthen, then surfacing resin is almost absolutely perfect. It takes no extra effort to thin to brushing consistency as it mixes to that consistency, and it adds considerable strength.

Now, if all you want to do is thin epoxy, as the argument above had spun off to, then use acetone.

If you plan to paint the airplane, use paint.
If you plan to fuelproof the firewall, use surfacing resin.

If you plan to read any more threads, plan to see grown men start spitting fights at the drop of a post.