I wanted to mount my camera to take photos through the windshield of my truck. I considered building something but saw this clamp on Amazon:
Amazon.com: Pedco UltraClamp Assembly: Sports & Outdoors
It works after a few minutes getting everything in the proper position. My 2002 Nissan Frontier has a pretty solid handle on the passenger side A pillar. I was able to clamp it there and mount the camera upside down. The orientation sensor doesn't mind. I didn't test to see if video works. As a backup, I looped the strap over the sun visor, so if the clamp failed the camera wouldn't fall. The camera was secure, but I wouldn't expect tripod-type stability from this type of mounting. My truck doesn't have a smooth ride anyway.
I did a quick test of some night shots, setting everything in advance and using a remote to fire the shutter. Here's one taken while turning: