The Garmin Dezl GPS accepts a camera input, so you can make one screen do double duty. Last fall they came out with their own camera option - camera wire runs to the front of the RV, which then goes to a wireless sender to be picked up inside the cab and displayed on the GPS. For the Dezl, it does not have to be one specifically from Garmin. It is kind of a hunt to put together your own system for it, though.
2012 Ford F-150 Eco, Max/Max
Jayco 26.5 RLS, Reese Sidewinder