I have one mounted on my back ladder, however I ran an audio video cable from it along the underside of the trailer and put the transmitter under the nose to keep transmit distances short. I used thin conduit strapped to the ladder to get the wire down. That way i was able to use a $15 wireless transmit & receiver combo from China on ebay and still have a crystal clear picture. I bought all my parts separate. The important thing is a monitor that you can reverse the picture on.
Here is all you need for less than $100
LINK50 ft RCA cable fro running(along underneath (just split them up and you have 2 spares)
LinkI pulled 12 v for the camera & the transmitter of running lights at the front & back of the trailer (accessed from underneath). That means I have to run with the parking lights on. No big deal. I will take some pictures today and edit this post with them