There is a big difference between cold raw fuel and hot exhaust. I had disastrous results with a Rustoleum finish on a Stick 40 Plus - the plans actually recommended it. It cured for at least two weeks, and in a test with cold fuel it seemed fine. But in a few weeks of flying the paint downstream from the exhaust, all the way back to the tail, turned into a gooey, oil-soaked mess. Jim