I thought a bit differently with mounting my GPS and decided to make use of our weirdo windows-within-windows
...........................
.......... it is a Uniden GPS with a 4.3" screen and where it is mounted does
NOT obscure the side mirror and checking the screen is no worse than checking the mirror. The extra power lead length required to open the door sits nicely between the door trim and the side of the dash when the door is closed. At the moment it is plugged into the ciggie lighter and I have to get 'round to tidying where I've run the power lead.
For reference this the view from the outside of where the suction cup is.
Please note the photos have been flipped so as to not confuse the majority on the forum who have the steering wheel on the wrong side.