The origional Floquil RR paints were a laquer which were designed to be used on metal and wood. They had their own thinner which was called dio-sol. They were definately not styrene compatable - if you brush painted styrene it would soften and craze the plastic. They eventually came out with a product called Barrier which apparently was a clear primer which did not react with the plastic and the paint would not react with the primer. However, if you used an airbrush and sprayed very thin coats, you could get very good results with Floquil RR paints on plastics. Only thing was, you weren't going to strip the paint if you needed to. Don't know if Dio-sol is still available - you might check at your LHS.
The few times I've used Acrylics, I've primed with automotive grey primer and it seemed to work ok