I tapped into the power for the three center rear identifier
lights. My original plan was to mount the camera a few inches below the center
light, but the styrofoam makes that kind of difficult and I ended up putting it slightly offset between two
lights and only slightly below them. You can see the small pilot hole I drilled before learning that the styrofoam was going to be in the way.
To get at the wiring, you can use your fingers to pull the laminate interior wall away from the ceiling carpet a bit and fish them out, crimp, then put them back. It feeds from the camera through a grommet (included in mine) in a hole I drilled in the body.