This lightweight (40g) dry box insert and optional lids (12g) are designed to fit airtight 4 Liter Skroam Cereal Containers. The airtight container combined with inexpensive hygrometer humidity sensors and bulk silica desiccant makes the ultimate filament storage solution. Links to these products are below.

Skroam Cereal Containers

Hygrometer

Desiccant

I recommend buying rechargeable desiccant. Fresh desiccant should keep your storage container at 10% humidity. Recharge the desiccant if the container is above 20%.

Version 2 Improvements

• Added a platform for the spool. Filament and spools no longer come in contact with the dessiccant.
• Added optional lids for desiccant holders to keep desiccant contained. Lids are 9 grams. Insert + lids is under 50g which means you should be able to print 20 inserts with lids from a single roll of filament.
• Changed orientation. The finger grooves are now on the front of the container which is more useful for filament storage. Thanks to @user_1517269923 for the suggestion.
• Implemented variable layer height to eliminate the need for supports. The top of the hygrometer opening will print at 0.08 layer height. No supports will result in a slightly rough finish but this area is concealed when the hygrometer is snapped into place.
• Refined geometry around the base to speed up print time and improve fit.

Version 2.1 Improvements

• Lids now press fit in place. Changes in geometry were made to the lids only. If you printed your inserts from the V2 print profile, you will only need to print new lids if you want them to hold in place.