Denny --

Like you, I have a cache of Scalecoat I (mostly those great Pennsy and NYC
colors). In general, I have had decent success using Scalecoat I over
Floquil primer on styrene.

But beware that this is a form of Russian Roulette, and that somewhere in
the revolver is a bullet that will get you. Make sure your primer is well
cured before spraying the Scalecoat I. And do a test patch inside the model
to make sure that bad things aren't about to happen. And if the styrene in
your model appears punky, it probably is a poor risk for Scalecoat I (the
old Cannonball Car Shops freight cars and E&B Valley passenger cars come to
mind).

Good luck!
Bob Chapman