I am sure this is not a new idea but just in case any one has a little red green horse person looking for an easy and inexpensive do it yourself project.. Had a minor incident with my horse in my Mcbride two horse straight load trailer. It happened while i was driving and although I felt the movement in the truck I had no idea what was going on till I got stopped and opened the doors...Enough said, that little experience got me thinking that I should have a way to monitor what was happening in the trailer when travelling.....The solution was easy, Its called "Behind Sight". A simple after market back up camera from Canadian Tire. For a mere $160.00 and 30 minutes of my time I installed this unit in my trailer. Its wireless to the truck. A small transmitter that has a range of 30 feet was installed with the camera inside the trailer and was powered by wiring it into the internal light. As soon as the trailer is hooked up  and the vehicle lights are turned on the camera is running.  A small TV style monitor mounts to the dash in the truck and plugs into the cigarette lighter socket. Now I can see everything my horses are doing in the trailer when I am on the road. Even in the dark thanks to a night vision capable camera with a built in Infra red  light source.  Under two hundred dollars to get piece of mind when trailering horses. No duct tape required...