I have had a lot of success with my Nav-Tool set up with a license plate frame camera. My best advice is to not go cheap with the camera. I did the first time, and replaced it with a Boyo brand, and the results are significant. I also replaced my reverse lights with bright LEDs.
Ed
PS. I hope this doesn't break any rules BUT I noticed that NavTool isn't being sold on eBay anymore. I have an extra brand new in box NavTool for BMW so if someone is looking for one and can't get one, just send me a PM. Good deal, I promise.