Mount your hygrometer on inside of clear lid inside your dry box. I used super glue to fix it inside the lid. I will link the dry box and hygrometer I used below

Dry Box- https://www.homedepot.com/p/Husky-12-Gal-Professional-Duty-Waterproof-Storage-Container-with-Hinged-Lid-in-Red-248921/313861297 

Hygrometer- https://a.co/d/2omXMOV