This is my solution for inexpensive but safe filament storage.  With 2 printed parts and three non printed parts, you can have safe storage for up to 12 reels of filament, for a cost of about $50.00.

I used silica beads to control the humidity. The beads change color when they are exhausted, but can be recharged with a short trip to the microwave. The printed box for holding the beads is well ventilated on all sides as well as the bottom to maximize airflow through the beads.

I added a combo Thermometer and Hydrometer so I can keep check of the conditions inside the box. I printed a holder for the Hydrometer so it could be seen from outside the box and can be easily removed should the batteries need changing.

Here are links to the non printed parts.

Silica Beads:

https://www.amazon.com/dp/B0C6PG7F3H?psc=1&ref=ppx_yo2ov_dt_b_product_details

Hyprometer:

https://www.amazon.com/gp/product/B09N92NRYN/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&th=1

Storage Box:

https://www.amazon.com/gp/product/B084F25MJX/ref=ppx_yo_dt_b_asin_title_o01_s01?ie=UTF8&th=1