I didnt want to pay the $200 for a controller holder so I built this one, using a nice arca swiss clamp so it fits perfectly on the stackshot rail or any arca swiss sized rail. My fusion 360 license expired so I ended up building this whole thing using the free Microsoft 3d builder app that comes with windows 10, pretty silly but it worked out great.

The Arca Swiss clamp I used came from thepaulsimon https://www.thingiverse.com/PaulTheSimon/about
https://www.thingiverse.com/thing:2912399

Required parts:
2x M6 bolts
2x M6 nuts