Re: 156 towbar advice
Its not too bad of a job. The worst bit is drilling out the stud on the nearside from the boot.
I have a 2.4 JTD too, there is no heat sheild to worry about. Also with mine there was no need to remove and cut the bumper, it just presses up to it a little bit, I have a brink detachable (brinkmatic).
Electric wise I used a 6 way bypass relay, power fed from a fused lead to the battery. If you have the SW you could tap into the rear lighter socket for the lighting. If you have a saloon it is also possible to tap into the loom up front that would have powered the rear power socket (If your car has the wiring, most do). I also wired up the tell tale on the dash instead of having the annoying beep in the boot which is not great if you are driving overnight somewhere with littleuns asleep in the back.