You might want to take a look at the post by Skelly in the "reflective coatings" thread in this forum.

Here are some websites that mention various kinds of heat dissipating coatings (mostly for automotive use.)  Maybe you'll be able to get some info from them.

Gun Kote
http://www.metalcraft-ar15.com/accessories.htm

Automobile header coatings - heat insulating and heat dissipating:
http://www.hpcoatings.com

Other auto heat dissipating coatings:
http://www.nacsracing.com/Banshee.htm
http://www.ram-pro.com/PAGE12.HTM
http://www.sdl.usu.edu/conferences/smallsat/proceedings/13/tech-ix/ts-ix-4.pdf
http://www.hotrod.com/editorial/article.jsp?id=51120

The 'Why' you are seeking is simple physics, dont you remember from your schooldays, Black absorbs heat ! especially Matt Black... but remember that heat that has been absorbed has to go somewhere, and that is the substrate, this may in time have a detrimental affect on your external powder coating and could cause it to prematurely embrittle and fail. You could try and give the external a mirror finish, in which case it would reflect external heat, and be cooler.

The black paint inside has high absorption/emissivity and so absorbs more heat, which transfers into the housing steel and dissipates on its external surface.  Pretty elementary.
If you want the 3CR12 housing to emit even more of that heat away, you would also paint it a matt black.  However, if the sun shines on this new, black, external surface it will absorb more heat and could reverse the process, so this measure would need proper thought first, depending on where the box is located.

Low emissivity coatings are available too - they are used on cement and lime kilns to save fuel.  Companies like Dampney should have more information and I suspect a Google search will reveal others.

I guess my real question is...Does black bbq paint dissapate heat better than flat black paint?  If BBQ paint can resist higher temperatures, shouldn't it dissapate the heat better than flat black paint too!

Hi CADCAMMIKE,
   I am not sure of the make up in bbq paint verse flat black but I would think the bbq paint may dissapate the heat a bit better because it is designed to be used with higher temps.
I am a coating applicatior and we have a coating we use for heat dissaption that works great. It can be used for electical motors, radiators, air cooled cyl. and many other applications. We used it on a gentlmens Harley that he use to run flat black paint on. Our coating made his oil temp drop 40 degrees. This helped keep a lot of heat off of him in the hot weather as well as protect the motor. If you would like to see the coating go to www.xpcoatings.com If you email me I can give you more info. Hope this helps.
Glen