A video selector box with all the camera inputs and trigger voltages to change the out put to the monitor can be installed in series under the dash and the system will work fine. I can't remember the manufacturer of a very common one used but the model VCS1000 comes to mind. You might want to do some research in this direction.
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7