I designed the hygrometer mount to clip onto the M8 rod inside of the following filament dry box:
https://www.thingiverse.com/thing:4880348

It's not really stable, but it also doesn't drop when moving the dry boxes around.

The hygrometer mount is designed to fit the following hygrometers:
https://www.amazon.de/-/en/gp/product/B07JDSHD4Z/

The hygrometer fitting is a remix based on the following hygrometer stand:
https://www.thingiverse.com/thing:4727323 (CC BY-NC-SA 4.0)

I printed this model with PLA with 0.25mm layer height, 20% infill and supports on build plate.