I picked up fabric paint at my local autobody shop when I refinished my full doors. The paint worked perfectly on my fabric doors--no cracks, fading, anything. When I purchased my half doors, I used the same product. Worked wonders on my plastic interior panels as well.
Product: SEM Colorcoat. Here's a link to the product. Not where I bought it, but you get the idea.
Krylon Fusion is wonderful spray paint made to adhere to plastic. Also Dupli-color has trim paint in typical interior colors that works well. You just need to make sure they are CLEAN before painting.(probably lots of build-up of armor-all etc) Dupli-color also has an adhesion promoter that should be applied after cleaning, and before finish coat(s)
Here's a couple low quality pics of the final product taken with my iPhone. The paint only suggests that you clean the plastic with an amonia based cleaner (Windex) before painting, so that's all I did. They turned out great. I used two cans total.
36 hours of drying:
On my jeep. They used to be super faded grey. Interior look so much nicer as a whole now that everything matches again!
I can honestly say that I did less prep and post work for this paint than anything... ever. Even less than the time I blasted "HAMMERTIME" onto the bottom of the stop sign on my corner. At least for that I had to make a stencil, but I digress...
I only cleaned the panels with generic Windex and painted them. No clear coat afterwards. I used Krylon Fusion Satin black. Kinda wished I used flat black - it's a bit more glossy that I expected from a satin finish.
Does not scratch easily. I tried that on the bottom.
Like I said, I did exactly what the can said to do. I was simply communicating my surprise that was all the can suggested. In the future, if the paint starts to get ugly, I will re-post to this thread with an update.