RE: covering cowling
The time I had the problem was when I primed with Krylon, the painted with it. Then decided it would be a good idea to put on a couple coats of clear TopFlight Monokote fuelproof spray, Top kote I think it was. That's what did it in. I think the next time I need to paint a cowl or wheel pants, I'll do that before starting the build. That way they will be dry and ready to fly when the plane is.
Don