This is a simple humidity sensor mount for your filament drybox.
I've created this to fit the IKEA samla boxes, but should work fine with any transparant storage box.
It is designed around those cheap circular LCD temperature / humidity sensors you can get from Aliexpress. Once the mount is installed in your drybox, the sensor just slides in from the top and remains removable to replace batteries.
Mounting requires 4x m3 hex nuts and 4x m3 10mm cylinder head bolts (like you get in the prusa kit).