i personally dont rate plastic primer. its shit and doenst stick well, ive always used normal grey/whiteprimer on plastics,put a dusting coat on it first and then a thin coat when its dry an then youre ready for the colour/basecoat. if you check my thread ive used normal spray paint on my engine bay bits (cam cover, airbox, dizzy cap etc) and its come out pretty good, if you prepare the surface well and dont take any shortcuts it'll come out good. best to use a real hard wearing laquer too, i use upol clear coat, its quick drying if you put it on lightly, but settles nice and smooth if you give it a thick coat. ask fishy or rob bee-r on here, they were pretty impressed with the finish on the bits i did. i used the same method on my old n/a and the painted cam cover, airbox and inlet mani are still going well, and that was done 3-4 years ago.