I had mine semi-permanently mounted to the dash. I bought the GPS and the mounting bracket from Best Buy where they have a "installation" including burying the wire. They use a black plastic disc just wider than the base, and double-stick tape - then you can use the suction cup to grip it down. Eventually the tape will fail and must be re-taped. About once a month the suction will break free and the GPS will fall over - no problem in my case because the short wire keeps it from falling to the console.. --- This was on a model 2557. When I got a 6-inch model 65 the suction cup was wider than the base but would still hold the heavier unit for about a week. It barely clears the dash. .
I have asked but they will not sell you a disc. You might be able to improvise. A dash mount is better because you can get the unit closer to your line of sight. And by the way, the oily base may leave a stain on your dash.