Got one of these from J-Car today. The flange mount is integral to a removable spacer, so you can flush mount it with a 22mm hole. It has a built in 5v regulator, and an inline fuse, so a ready to go solution. The depth if flush mounting, is about 30mm. I am fairly sure I have room for a couple of them behind the interior light of my Pajero. Beats the heck out of butchering a cigaret lighter plug with USB socket, and probably costs the same ($14)

Just need a dash cam to plug into it now :-)