This is what I use for my point and shoot. It's OK, but it does bounce around a tad. I tried using it with my D7000 and a 28 2.8 prime (light weight), but it bounced around way too much for the footage to be usable.
Here's some footage I took using it with the point and shoot mounted to my left fender. It holds like a champ! I just wish it had less flex in the arms. There are much more expensive systems out there with multiple cups, etc, that are meant for DSLRs.
This month's issue of "Outdoor Photographer" has a special feature on shooting from a vehicle.
They offer 3 direct window solutions, Kirk's MP Window Mount, Puffin Pad& The Pod.
Check the issue out on line or in a store.
Dan
Check your state vehicle laws, they may prohibit or restrict attaching devices to the windshield. Not sure about dash mounting but that would seem less an issue assuming it as safe, sturdy, didn't obstruct vision.