My backup camera is mounted on the trailer and my only complaint is that the video signal is weak. The problem is that the kit came with 100' of unshielded cable, which I used.
To correct the problem I am going to install regular shielded video cable, similar to what you would use for your VCR, just very long. I have tested it with a short run of shielded cable and the color and clarity is excellent.
Also, be careful running your power supply to the camera. Do not run it in the same strand as the turn signals or brake lights. I get a little interferrence from my turn signals.
Having a camera on the trailer is a huge benefit in traffic. I sure makes merging and passing much easier and safer. It helps too in backing the trailer obviously.