prep job includes
a good sanding job. if the plastic has scratches in it, remove them by wet sanding. start out with a low grit number like 200ish and work upto 1000.
you want the space you are painting to be around 75ish. paint does not want to stick when it is cold and wet out.
bulldog adhesive promotor is some good stuff, it is used when painting plastic bumpers on cars. just do not sand through or your paint job just went to sh*t.
when painting to light coats. get around 4-5 coats before you wet sand again with 1000+grit paper, lightly sand it, like said before, you do not want to sand the adhesive promotor. after a light wet sand, add a couple motor layers of paint and sand again if needed. then do clear. put around 3-4 layers of clear, sand if needed and clear again.
it is best to let each layer of paint and clear dry before you add another layer. so paint one light layer, go inside and play a game or two of COD then check paint. or you can look at porn, whatever you want to do to pass time.
whatever you do, do have the space heater pointing directly at your plastic, it will not be good for the paint that is drying.