I spent some time digging into silica drying media.  I consulted one industry customer, and a quality control engineer, if the cereal box is 4 liters (let’s not fuss over the area taken up by the spool of filament), and using the “common” industry standard (3 ft^3 will be easily kept at a state described as “very dry” using 40 grams and kept sealed).  To keep your cereal dry box’s 4L “very dry” it requires 0.015g.  I bought a bag of 5g pouches (100 @ 5g ea. $9.50) and chuck one in.   Thoughts?