Plastic skirts, how to paint them?

I have a 24 year old car with a "plastic skirt". Basically it covers the lower part of the car body from the elements. I just removed them because the paintjob was heavily weathered and would like some input on how to properly repaint them, especially what type of primer to use. Generally i am using the Spraymax 2K system on my car and i actually have a 1K plastic primer from them also but want some more input on this.

Any thoughts how to approach this?