I ground mine to the glasses pocket screws, left the USB convertor up there too. I ran the ground wire up and DOWN through the hole so when i installed the screw, it would stay if i ever had to take them out, so it wont drop out. Obviously ran the power wire up the A pillar from the fusebox.
I got one with 2 USB ports, but here you can buy one with the end on it already.
I then installed the USB port in the camera housing