I have both headlights out of the car; taken apart; chrome removed; and I am prepping the plastic for painting. I intend to sand the plastic with probably 400 – 600 grit paper but I am wondering about priming the plastic before I paint it. The paint I have bought is Sherwin Williams for the base and clear coat. Also, need I add to the mastic when I put them back together? If so, what mastic do I use?