Hi,
I had a look at the OEM Volkswagen Parktronic, it is only with a buzzer/beep only so I decided to go with a similar one. I have bought the ParkitRight kit from their Ebay shop, as I intend to install it in the lower par of the bumper I bought theirs as the sensors come unpainted and the plastic colour is identical to the lower part of the bumper.
I had a failed go last weekend, I got the C-pillar off without breaking the little airbag cover tag, removed the panel, but for the life of me I couldn't identify the correct wire as I didn't have a volt-meter. I could make the kit work by attaching the kit-power-wire to the reverse light directly but as the light is in the tailgate I need to find it behind the c-pillar cover. Once I can sort this bit out I'll be brave and drill the bumper, from feeling around behind it there is the actual bumper bar behind the cover so location of the sensors will be important.
Weather depending, I'm going to have another try this weekend, I'll try to take pics as I go unless it turns in to a complete disaster and I end up crying for a month.
By the way the kit I bought was the 4 sensor kit from ParkitRight, though they have a web site
www.parkitright.com where you can by for £58 you can get it from their ebay shop Parking Sensor Superstore for £29.50.

Dave N