Dunno about the D4 but the D sport has a large grommet coming through from behind the passenger glove box.
A piece of welding wire with cable hooked on the end can pierce here, just ensure it away from existing wires, and pushed through.
The camera on rear of my D2 is bluetooth. Wire from camera to box inside light aperture, operated via reverse light.
Camera has it's own supply with receiver aerial. Nothing in-between. Worked well though I did occasionally pick up Eastenders ? Honest ! That cost £15 from classic show couple of years ago.
