Painting Plastic Fender Flares

I have some to go on my truck and I'm painting them to match. They were off a wreck, so not in the best of shape. I cleaned and sanded them, sprayed them with adhesion promoter, applied high build primer and wet sanded them with 800. Now they are nice and smooth and ready to paint. Someone told me that it would be a good idea to spray more adhesion promoter on top of the primer. I've never heard of this. Is it true?

Spray right over the primer.