Krylon Fusion is designed specifically for outdoor plastics - no prep-work is indicated on the can (though I always reccomend a quick wipe-down with paint thinner or alcohol to remove any oils or gummies that get on surfaces. Only down-side is the limited number of colors currently available. Check out my gallery to see the result (there is at least one pic there of the interior paint.) Biggest thing for diy-ers - practice on something throw-away but as similar in material as possible first, to get comfortable with the product (buy a cheap piece of plastic/plexi at Home Depot or Lowes). When ready, make sure you have a clean, wind-free environment, and take your time. Multiple coats is not a crime if the color is a bit thin the first time, but make sure you allow each coat to tack up appropriately first. Nice, smooth, even passes with the paint each time from 6" to 12" away, and try to not have over-spray too much (I sometimes use a fan at a distance, to get a very gentle air movement, to carry overspray off).
Good luck!