I suggest wide angle lens so you can see from the ground to overhanging limbs above. If you drive a lot of miles per year you may want a more expensive one. If weekend camping my cheap Pyle brand mounted on top of the license plate has an excellent picture and color after 9 years.
I have my camera wired to be on whenever the engine is running so I can see small cars or tailgators behind me on the highway. Wireless cameras would seem to be the easiest but they lose the signal near airports, electrical substations, or truckers with high powered radios.