Reddit mentions of Rust-Oleum 209460 Plastic Primer Spray

AFAIK, most plastics have a coating that protects it, but also prevents paints from adhering well. To get paint to bond to it you'll want to scuff up the surface with a rough material (like a scouring pad from the back of a kitchen sponge. Or fine sandpaper if you're brave).

After roughing it up, wipe it clean, then spray on a plastic primer (it's basically a "spray paint" that's just alcohol and thinned out glue, generally clear or with some white color), and then finally, apply the final paint once that dries.

this primer works well for me
https://www.amazon.com/gp/product/B0002YTW8K/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

here is a finished paintjob
http://imgur.com/gallery/RucQV2x