You just need some kind of GPS mount you can mount your iPhone to? Get a GPS mount and mount your iPhone to it.
I have also seen rechargable flashlights that plug into the cigarette lighter. You could get one of those and gut it, splice in your iPhone cord, put some velcro tape where the lense is, some velcro tape on the back of the phone and violia! A charger stand that plugs right into the lighter socket.