I missed a piece of information out here, and a couple of pics.
If anyone was wondering how the CrystalSky is mounted to the lid here:
I’ve used a simple magnetic mount.
On the back of the CS is a wafer thin stick-on metal plate, you could do the same thing for an iPad or any other tablet here too.
Sorry, seriously oversized pic here!
Then on the lid is a super-strong magnet of the same size.
Hassle free 
It also means the original DJI quick release mount on the bottom of the CS is unaltered so it can still be connected directly to either of the controllers when you need to be portable still.