painting exterior plastics

Not quite the same thing but when my shop was built the windows were white vinyl clad & I needed them green to match other trim. I cleaned them (I think with mineral spirits) & then painted them with canned spray paint specifically made for painting plastic & its held up perfectly through 4 or 5 years of nasty winters & hot summers. No noticeable difference/fading/peeling etc.

I'm with RedFish, I think it's all in the prep & using a paint made for the plastic.