I ended up going the cereal box route for some dry boxes but wanted to avoid cutting/drilling any large features. Realized the spout was perfect for mounting a hygrometer with a simple bracket. Most of these containers have integrated gaskets, so a little bit of adhesive around the sensor should allow for a good seal to be maintained. The bracket also allows full access to the battery compartment on the back.

The bracket is designed to fit the common cereal containers and round hygrometers all over Amazon. In my case, the bracket was sized for a 60mm spout opening and a ~40mm sensor body. The sensor should snap in with a snug fit and the entire bracket will then press-fit into the spout of the container. There should be enough room between the sensor and inner wall for some adhesive if you want to maintain a good seal. I have included the parameterized Fusion 360 CAD file if you wish to customize it.

Recommended material is PETG or even a hard TPU like 95A. Three or more perimeters, at least enough that the inner wall around the sensor is solid. This will allow the bracket to flex a bit when snapping the sensor in without easily cracking. Can be printed face-down with supports needed on the inner rim. The example was printed in some Bambu PETG-CF that I needed to burn.

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