It seems this type of "cigarette lighter" 12 volt Milwaukee tool battery charger would be good on a service truck. But if one wanted to mount it on the truck bed somewhere it would have to be waterproofed. I googled, but couldn't find an enclosure. 

Does anyone know of, or has anyone made a waterproof enclosure to allow it to be mounted outside of the cab? Getting the 12V isn't a problem. I understand the enclosure might have to be vented, but that's probably do-able also.

Link to Milwaukee 12V charger