Reversing Distance Sensors

The previous photos clearly show one feature of the Vito van: no windows in the cargo part of the van. Well, yes, that's what I opted for in the first place. However, reversing is somewhat slow and one need to be extremely careful. The previous owner managed to get a severe dent in the right rear door.
Actually, even changing lanes also needs extra attention, but that's another topic all together.

Reverse parallel parking in front of my house is relatively easy, since I got a nice maple tree in my front yard, which is a perfect visual beacon when looking through the mirrors whilst reversing.
However, some more info would be such a good thing.

Hence, I decided to order an aftermarket distance sensor system. Initially I thought about a camera, however, there seem to be limitation to those cameras. So, a sensor system it is!

After having looked at tons of reviews, I decided go order a relatively simple one from conrad electronics:  Parking aid (corded) Rear acoustic, visual CE

The scariest bit was to drill the holes in the rear bumper. I wanted to remove for doing said task, however, I was unable to loosen the screws, hence, I did it blindly. And yes, I could have oped for marking everything properly and stuff... but that's not me. Holes are in, so so, but who cares?

The hardest thing turned out to find a route for the sensor cable to the inside of the vehicle. For now those cables are just routed from under the rear bumper, over the same and through the left rear door. 
I figure, I will just created a passage through the rear bumper as to better hide the cables. Never the less, those cable will be are routed between the rear door and the door frame.

Photographs will follow! So, stay tuned!

UPDATE:
The pictures I promised. The solution is not pretty, as stated above, but, it get's the job done!

the 4 sensors - the dent in the right door was achieved by a previous owner

cable routing - small hole in the bumper, right at the red electricians tape is