*Quick update* Finally got around to installing my rear sensors. Big thanks to everyone for their help, especially Dave for his measurements - although I did modify the centre sensor dimensions from 90mm to 70mm (or approx 50mm if you measure from the top of the flat section of the bumper down). Visually 90mm looked too high for me. Overall I'm very happy with the install and the sensors work a treat. Install did take some time, but that was mainly due to unknowns on how to remove trim panels, determining wiring etc. For anyone interested I installed the control unit to the passenger rear side, below the plastic cubby box on that side. There's a rubber grommet perfect for bringing the wires in and an earth point right in this location. I tapped into the reverse +ve wire (from memory this is a blue wire) behind the access panel on the left, keeping close to the main wiring loom so as not to get in the way if/when I need to change the reverse bulb. I then ran the speaker wire behind the passenger side rear trim panel and placed this behind, just above the 3rd row seat cup holder. If you take a look there is a small access panel in this location. My speaker has two volume settings, low and high and an off setting, so being able to access it here is perfect. Speaker is currently set to low which is more than loud enough for me. If anyone has any specific questions just ask away - hopefully I can help.