Picked this up cheap and dirty unit.. wire the camera into the reverse lamps ..or wire it into your trailer plug. Monitor sits on left hand side of dash and plugs into cig lighter.
Picture is good for $99.00 and free shipping ...and it's wireless..
http://cgi.ebay.com/VR3-WIRELESS-COLOR-BACK-UP-SECURITY-CAMERA-DIGITAL-2-4_W0QQitemZ220107741021QQihZ012QQcategoryZ48605QQr dZ1QQcmdZViewItem