Metal paint would be a rather heavy-handed (and messy, and not very durable) way to do it; fortunately, you don't need much conductivity at all. What's good enough? Supposedly, average everyday dish detergent!
I don't know how well it'll stay smeared onto a plastic surface, or if it will be absorbed and require re-treatment, or what. Or what the lasting effects are, in contact with electronics.
It sounds like you're extremely paranoid about a very simple thing. If I had to store very sensitive electronics in that type of container, I would store boards individually wrapped with metallized mylar or other antistatic bags, and call it done. That's good enough for shipping them in cardboard boxes, after all.
Proper handling is far more effective than having approved ESD equipment around. When picking up a board, touch a known ground point (screw terminals, connector shields, etc.). Avoid sensitive (data or otherwise) connectors, or touching components directly. If nothing else, carry the board by the edges to avoid touching anything at all. When placing the board on a conductive surface, or installing in equipment, touch that surface first. If you're sitting in a chair, beware that shifting your weight can induce static; ground yourself whenever you move.
I've never had a failure I can attribute to static charge, following these procedures. Touching things carefully and avoiding static is as natural to me as, say, avoiding germs is to a germophobe. In both cases, there's a specific set of gestures you should follow, and those you should avoid.
Assuming you already follow this sort of procedure, the only thing ESD mats grant you is the ability to handle extremely sensitive electronics, like naked micron-scale CMOS gates (maybe a concern around GHz RF work, but other than IC fabs, not much?). Reason being, even with a ground to discharge to, the transients (induced ground differential, induced electrostatic) may be enough to cause problems, and the extremely high resistance of ESD material discharges those potentials gradually, avoiding those transients.
Tim