I found that the TurtleNeck mount bracket on ArmorTurtle/TurtleNeck Github was too loose to hold the TN upside down when mounting it to the Box Turtle itself (like Steve Builds did on his build).
Borrowed the idea from @ViktorvonDue's TurtleNeck magnetic mount but redesigned a new mount similar to the stock mount but with 4 magnets that are aligned with the TurtleNeck screws to hold it more firmly.
I also took the opportunity to make the mounting flange wider to accommodate a M3 roll-in T-Nut, which was not possible on the stock design.
You'll need:
Inspiration:
https://github.com/ArmoredTurtle/TurtleNeck/blob/main/STLs/TN_horizontal%20mount.stl
https://www.printables.com/model/1191141-turtleneck-boxturtle-magnetic-mount
The author marked this model as their own original creation.