Carlos,
I've used "hot" paints and primers for many years on sytrene, and never had a problem.
I always make sure I "dust" on the first few coats of primer, then hit it with a quick wet coat. I allow adequate drying time between all coats.
Then I do the same with the top coat, dust on a couple of coats, then usually a max of two wet top coats, and the job is done.
I've never had a problem with the styrene painting this way, although there are some fillers that are a little sensitive to the paint, so it's best to experiment with them.
Cheers,
LeeTree