You might check some catalogs or online retailers that sell car/airplane powered dc adapters for laptops. I have one I bought a couple of years ago that is perfect. I cant remember where I got it but these are the basics. It takes a 12 - 16 VDC input. via either a cigarette lighter in the car or with the additional adapter via the power plug on the seats of some of the newer airliners. The brick peice of it has an adjustable pot that can adjust from around 6 - 20 VDC output. The output end has a standard removable end (2 pin style). You can get dozens of different end pieces from Radio Shack as they are the same style end pieces that Radio Shack has for their AC adapters. I paid about $100 for mine. It sounds like it could be perfect for what you are looking for. Just hard wire the input side and feed the brick and output wire into the glove box.