Thanks for replying
On my car the nav is a DVD-based system and the disc is loaded behind a flap behind the drivers seat - this is the actual nav computer too. I guess it's similar in yours.
Since its in the boot (trunk) of the car then it would be an easier install because the reverse light feed is there, you could take the power from the nav computer and you don't need to pull the dash apart.
I'm hoping to buy one of these so I'll let you know how I get on