I haven't done it for a loooong time but I used to use Future floor wax with pretty good results. Not sure it's still around or not. Don't put it on the seat though....don't ask
Mop n Glo rules for most plastics. Get it clean first, then as many layers as you have patience for will really get you a deep shine. Always used it on my football helmets.
Jim Cook put me on to future floor wax for my black plastic on my 97.. Worked well and had this odd but pleasant smell.. also the mud wouldnt stick to it for a while..
Steve