I use the mount made by Logic Dive Gear. It is a swiveling, quick release system and can be had in both a large and small version. I have the large version and it works quite well with a GH4 or 5Diii system including a monitor and a pair of Keldan lights. It is capable of taking a larger system as well. The only bad thing I can say about it is that the large swivel mount is cut for the Genesis scooter body diameter or larger. If mounting to a SUEX scooter, you will need to perform a simple modification to make it compatible with the SUEX's slightly smaller body diameter. Not sure if Jon has updated the design yet to account for the SUEX body diameter. I had tried a DIY solution originally but as my system got bulkier, I needed something 'better' but lacked access to the machinery to build a proper mount myself.
Jon's scooters are also excellent machines and he offers some modifications that would make them even better if you did a lot of shooting from the scooter, such as left handed control and a dual handle option for driving a bigger rig around. The thumb actuated, infinitely variable speed control on the Genesis scooters makes on the fly speed changes very easy and without disturbance to an ongoing shot.