I found the trick recently. Get some old boards or something and sit them out in the sun. Now, in a vented, non windy area, sand the plastic down with fine sand paper and blow off the dust. After you rough it up and smooth it out, wipe it with a wet towel. Dry it perfect. now, spray color on lightly until the color is solid. After you have the color looking even and how you want it, clear coat the hell out of it. I probably sprayed about 3-4 nice coats of clear. I need to re-do my older pieces now that I have the technique down better.