The 4200 doesn't have an undertray. The back bumper is a piece of p!ss to take off but can be a drag if you don't know where all the bolts are. There are 3 x 10mm wing to bumper bolts each side which can be accessed by removing the boot liners. The ones on the drivers side are behind a plate, which mounts some relays, held on by 3 x 10mm nuts. There are 4 star drive bolts (visible) along the top of the bumper and two, IIRC, 13 mm bolts underneath the boot floor next to, and above, the rear boxes. There is a screw at the bottom of the arch liner on each side. When all these are removed, pull the sides of the bumper out, but not too far, and slide the whole thing back. If you need to, you can then remove the parking sensor lead which goes to a box next to the right rear light box. Assembly is the reverse of the disassembly.