The Jotto mounts look to be very high quality. Will definitely look into those. Is the part that actually holds the tablet custom-made, @LandCruiserPhil ? I found the articulating swivel but not the top piece just behind the swivel.. http://jottopublicsafety.gojotto.com/articulated-swing-arm.html
Jotto mounts are top quality and used by many law enforcement and emergency vehicle. I custom make the lower post mount part. The iPad is held on with velcro. Been using the same top mount in my 80 series for years and thousands of off road miles with zero vibs and the pad has never move from the velcro.