I make my own as well.
I start with 1/2" thin walled PVC piping cut to desired length 6"
Take two end caps (non-threaded) and drill three 1/32" holes in a triangle as near to the center as feasibly possible on each one
I then soak (in a 50/50 mixture of distilled water & PG) Polymer Crustals (hydrogels - crystals that absorb several times their weight in water - white/clear in color and can be purchased at any landscaping/plant store (once they absorb water they look like globs of clear jello)
I then use the end caps to 'punch' plugs of the green florist bricks (already cut to a 3/4" thickness) and soak then in the same solution.
Place one green plug into a cap, placed cap upside down on table (while wife isn't looking) and tap the pipe/tube snugly into the cap
Now fill tube with hydrated jello crystals (leave 3/4" minimum from top for other cap
Now place green plug in other cap and tap onto other end of pipe.
Works great for about a month for up to 25 sticks in a used cedar cigar box or other types of travel humidors .....
p.s. You can also recharge them and they're less than $2.00 each to make (cheaper to make in bulk).