That looks neat.
One of these adapters indoors would be handy as well to keep it charged, if you decide to get one for home use (save draining the car battery!).
Mains AC to 12v Cigarette Socket Adaptor Power Supply on eBay, also, Power Plug Adaptors, Accessories, Consumer Electronics (end time 13-Dec-07 18:00:00 GMT)
I got one to use 12 volt items (car vac etc) off the mains and charge phones etc that only come with in-car cigarette lighter adaptors. Works well.
Ps: You can buy them from the sellers shop if this auction is closed by the time you view it.