Well I'm about to get started!
Took the opportunity to wire in the powered DAB Antenna too. 31 Stations found as supposed to 0 from my driveway, which is in a bit of low ground. Tapped in to the 12v from the back of the unit. Also much neater than the passive one which took up the entire height of the windscreen.
Cheers for the guidance ppavuk, I'll let you know how I get on.