After much deliberating I decided to fix my Garmin sat nav (nuvi 250w)to the windscreen using the sucker mount provided(you can use the dash disc if you prefer) keeping it as low as possible on the window,so that unit was almost touching the dash when vertical,sitting just behind the domed top air vent.
I then connected the charger cable and fed it towards the windscreen where there is a rubber flap, where the windscreen meets the dash and I pushed the cable under the rubber flap using a blunt blade and ran it along towards the passenger door continuing along the seal inside the door which runs down the glove compartment down to the footwell where the orginal cable ended.
At this point I connected the orginal charger to a 3m cigar lighter extension cable(£4), hid the connector behind the upholstery in the passeseger footwell just to the left then fed the remaining cable across the passenger footwell to the bottom left of the centre console.I then removed the bottom upholstery panel(just 4 retainers) tucked the excessive cable behind ,fitted the panel back and plugged in the connector to the cigrette lighter socket.
I now have just about 1/2" of cable showing at the connector and approx 5" showing from the unit to the windscreen.
I bought a black carbon effect non slip mat(£2 from wilkinsons) and placed it on the dash under the unit with the cable underneath it and now you can only see approx 2" which goes over the windscreen vent.When you don't require the charger cable you can disconnect it and run it along the windscreen vent and it is hardly notceable.
All in all a very tidy installition for a small outlay,well pleased.