Those are cool, although I don't think I can convince the client that 13 qt rounds up to 55 gal.
I did some searching, and found video of the process of painting plastic automotive parts. Extensive and expensive, but an option if they really want it to last. Otherwise I proposed scouring with sanding compound, and lots of cans of Krylon Fusion. If I get the job, I'll investigate a non-rattle can product a little further.