After reading all the advice and horror stories I could find on the forum, I tried painting my first FUD products - two ship models and a model of a Bloodhound missile. I washed all three with warm water and mild hand soap and let them dry thoroughly. I primed them with Game Color white acrylic primer and let them dry for several days. I painted the ship models with enamel paints (that's what I've been using for the last fifty years). I'm almost done with the ships and things are going well. When I tried painting the missile with white enamel, it seemed to dissolve the primer. I scrubbed the missile as best I could with paint thinner and put it to soak in brake fluid. (That's the most benign way I've found to remove enamel paint from plastics.)
The only difference between the ships and the missiles is that the former got two coats of primer, while the latter got only one. Should a second coat of primer make that much difference?
I'll let you know what happens to the ships after they're Dull Coated (I'm not expecting anything bad with so many layers of primer and paint on the FUD). I'll also let you know if the missile model survives the brake fluid bath.
I encourage designers of small-scale airplanes to offer all their products in WSF. Detail may be lost but WSF seems to be a much friendlier material.