The steps are as simple as drilling small hole in the camera's water proof case to allow access to the USB charging port. From there, you can supply constant power through a 12-volt USB adapter. Mount the camera to your windshield using the suction mount and you're very nearly ready to go.
Next, set up the loop recording feature and you're good to go. The Hero3 can loop record in 5, 20, 60 or 120 minute files wherein it will record to the maximum time before starting a new save file. Once the memory card is full, it will record over the oldest file. It can also loop record in "maximum" mode, where the camera fills the memory card, then starts over again. Check out the video Translogic made below for a look at the finished results.