Thanks for the great discussion everyone-- its obvious that there are many ways to configure one's setup!
I ended up getting 2 Nauticam arms (75mm double ball arms) and a standard multi-purpose clamp (with the ball mount attachment) to run off of my extra housing mounting points. This is most similar to the second photo I originally shared without dealing with the triple clamp. It provides quite a bit of flexibility for running the monitor in the above, behind, or 45 degree angle configuration.
There is extra room below to run the controls, and allows the monitor and HDMI cable to tuck in quite nicely behind the camera housing. An additional benefit is that it allows me to more easily control buoyancy in the shallow environments I frequently work in and still have independent lighting control.
Let me know if you see any ways to improve upon the design here!