Holds those cheap rectangular temperature and humidity meters from ebay, aliexpress, temu, etc. Unit easily slides in. Can be printed in PLA or PETG. I liked Matte black PLA personally.

There are grills for the moisture to react the unit through this model. Optionally If you want to accelerate the response to humidity, you can open the hydrometer unit and drill some small holes in the back. This will let air diffuse in and out much faster.