First off I removed the piece of dash that holds the 2 vents. I then made a L shaped bracket from aluminium sheet and bolted the stripped down Garmin mount to this. The bracket was then pushed in between the bottom of the vent and the dash. I drilled a small hole through the dash, bracket and vent and fitted a screw to stop the bracket sliding back out. The vent is blocked off with a piece of foam and the power cable goes through the vent and comes out of a hole inside. The holes and screw are effectively hidden once the dash is reinstalled.