GeraldO...do you ever wonder why practically NO ONE has heard of or used this epoxy-over-paint method? Surely there is a good reason...don't ya think?
Perhaps Krylon isn't fuel proof, but it's probably not enamel either. If it's a quick-dry paint formulation, it's likely acrylic lacquer. There are a variety of enamel formulations in spray bomb paints out there. There are acrylics, alkyd, latex, epoxy, and various synthetic enamels. Black Baron Enamel is fuelproof. I have read that several colors (not all) of Rustoleum enamel are fuelproof. Dupli-color automotive clear engine enamel is supposed to be as well. I do know Krylon isn't meant for glow fuel, at least not as a finish coat. Otherwise, we'd all be using it as a finish coat since it is relatively cheap, compared to epoxy enamels, which ARE fuelproof. I was generically referring to epoxy enamels in my post, not the cheapo acrylics or alkyds.
Bottom line, I still think that if an epoxy topcoat were to be used, it would be best to spray a two-part epoxy, or a catalyzed automotive paint that is DESIGNED for such use, like the HobbyPoxy paints and PPG automotives. Most epoxy glues that I have used don't set hard, unlike epoxy paint. As for yellowing, no epoxy glue I have ever used has remained clear after exposure to sunlight for a few months. Automotive paints have UV stabilizers added in. Epoxy glue doesn't.
There are solvent-based polyurethanes and water-based polyurethanes. You might have had better luck with a water-based one than one out of a spray can. Testing compatibility first on scrap before committing paint to model is invaluable, needless to say.
If you feel like the epoxy glue thing would work, a simple test can be done. Mix some up, thin it, spray it over Krylon, and see what you get. Might be interesting to weigh the piece before and after the process. Of course, after it sets, you're stuck with the results, good or bad.
I personally don't have the time to waste in my hobby trying to use products for purposes for which they weren't designed, risking questionable results. I prefer to use the right materials, and get it right the first time, with predictable, repeatable results.
Just My Humble Opinion. Your Results May Vary.

Rick