Would one of the polyurethane bed liner materials work? Black is a standard color for most. Rhino has sprayed the exterior of vehicles quite a bit. I dont know the smoothness for each brand but you can get or view samples from most of them.

The real stuff is filled with solids like the adsorbing foam.

By the way, according to my buddy at PPG, most automotive paint is shipped to the auto manufacturer in big containers that are about 400 gallons (as I remember). The container is a big cube instead of a drum. The microwave adsorber may ship in drums.

mike in tucson