We dont have the luxury of having so much stuff available to us in our local shops...so I made my own.

simple_ - bought a security camera from a local alarm installer...the type you would mount outside to monitor a gate or something like that...it is really small and was cheap. I wired it to the trailer 12v power supply (when pluged into the tow vehicle) and used a spare pin in the trailer plug for the signal.... In the truck I used a standard DVD screen....

It works like a treat and gives me peace of mind that the horses are fine in the back. and it cost very little.

Good luck..if you need more details, just shout