You can get wireless units, both camera and monitor need power but there is no wire running between them. The monitor and camera are powered from an ignition controlled source, there is one on the light switch for the monitor and the camera is powered from a ignition powered source. If you have daytime running lights you use this.
Having the camera in the car will give you poor visibility of the outside.
I mounted my camera between the hatch opener and the license plate light and ran the wire through a small grommeted hole I drilled beside the camera. The wires go up through the rubber grommet at the top of the hatch and out into the trunk behind the top and bottom trunk liners. The power comes from my daytime running lights.
Post showing camera installation. CLICK
Post showing fitting of wireless camera. CLICK