I haven't done that, but there have been some interesting methods. Krylon rattle can, spray on bedliner, powdercoating or anodizing - (more cost unless you have a friend), and talk about having a vinyl wrap applied to just the aluminum panels. Another option that may or may not appeal to you is covering them with black reflective vinyl.
http://www.ebay.com/itm/like/130885649664?lpid=82&chn=ps
The 3M Scotchlite products are black in daylight and vividly reflective at night, looking a brilliant white that really catches light from far back. They offer it in panels and rolls. Here is an example I found with a quick search for black reflective vinyl.
LINK
The accounts I've seen on the forum all took their boxes apart to just do the aluminum panels and left the plastic parts alone.
Hope that helps.