Original Biggles

I own a 2011 Outback 2D with Sat Nav. I tow a caravan which is 7ft 4in wide. Sometimes I get small cars or motor cycles in the blind spot when they are close to the rear of the caravan. I have a wireless camera (as used in aftermarket fit for reversing cameras. The Outback has its own reversing camera but it cannot see through the caravan and it only works in reverse)
I have connected the camera to the Aux video input to the Sat Nav. This works well when parked but as soon as the car moves forward it is inhibited. This is done to stop you watching DVD's on the move.

Is there a quick/easy fix to enable this function. I believe the use of a rear view camera, which has the same function as a rear view mirror, is legal.
Any suggestions welcome.
Bob

originalbiggles@talktalk.net