I have had good luck with ProClip.com for GPS mounts in my SSRs and Envoy. They have a 2 piece process where you order a base for the vehicle and a holder for the item to be held and the work together so you can move the holder from vehicle to vehicle.
I use the Nexteck Magnetic mounts. Makes it easy to move from car to car. The mounts are available in several different attaching configurations, but the one that attaches directly to the dash with a thin double sided tape works best for me. Available on Amazon