You could go two different directions with this for a fairly low cost and minimal amount of intrusion. Either a camera that mounts on a license plate that you can feed into you current rear camera monitor or the ultra sonic distance alarm. I would go with the alarm that beeps when you get close to something. Taking your eyes off the road to watch the camera display kind of defeats the purpose while with the alarm you'll get an audio feedback. System doesn't care which bumper it's mounted in (front or rear) still works the same. Just add a switch to the dash to turn it on or off rather than working off the back up lights to trigger it. Amazon has sensor packages for less than $40.