The problem is the industrial enamel. It has some hot thinner in it that is causing a chemical reaction with the old paint, off gassing. Most likely this is the source of the bubbles. The driers helped as it speeds up the dry time, less time for the chemical reaction. Right now all I can think of is priming the surface first (before painting) and allowing the primer to dry really well.
If I can think of anything else I will try to remember to post it.