(purchased parts through Amazon are affiliate links)
(1) 4 inch 5/16 bolt (or 8mm threaded rod) (bought from hardware store)
(2) 5/16 nuts (or 8mm nuts for threaded rod) (bought from hardware store)
(1) PFTE Tube Cap (download in files)
(2) Rod End Holders (download in files)
(2) 8mm x 22mm x 7mm Bearings - http://amzn.to/2G9QKUU
(2) Spool Plugs - https://www.thingiverse.com/thing:2773587
(1) Cereal Dry Box - http://amzn.to/2toGOnq
(1) PC4 M6 PFTE fitting - http://amzn.to/2oZLieN
(1) O-ring if your fitting does not come with one. (bought from hardware store)
(1) Cup of Orange Indicating Silica Gel Beads Desiccant - http://amzn.to/2oUmdCL
(#) Any length you prefer of 4mm od/2mm id PFTE tube. - http://amzn.to/2oZLieN
Step 1: Measure the bolt to the width of where you placed the Rod End Holders inside the Cereal Dry Box and cut off the head of the bolt and any extra length of the bolt.
Step 2: Measure where you want to place the Rod End Holders inside the Cereal Dry Box, you want to make sure that the spool has enough room from the top so that you can close the dry box, and far enough away from the ends so that the spools don't rub.
Step 3: Depending on what kind of glue you're using, you may need to scuff up the inside plastic so it gets a good hold. Glue the Rod End Holders inside the Cereal Dry Box. These will be used to hold the spool in place.
Step 4: Assemble the Spool with the spool plugs, bearings, threaded rod made from the bolt and 2 nuts to hold in place on the spool.
Step 5: Pour 1 cup of Orange Indicating Silica Gel Beads Desiccant into the Cereal Dry Box
Step 6: Slide the spool into the Cereal dry box, pushing the sides out a bit to place the ends of the threaded rods into the Rod End Holders that you glued inside the box.
Step 7: Decide where you want the filament to come out of the box and drill a 5.5mm hole, be sure to deburr the hole for a better seal. Add the o-ring to the PC4 M6 fitting and screw the fitting into the hole.
Step 8: Push and lock the PFTE tube into the fitting, then thread the filament end through the PFTE tube. Place PFTE Tube Cap on end of the PFTE tube
Step 9: Secure lid of the Cereal Dry Box
I'm still not 100% happy with this box, but at the moment it's what I came up with. My biggest complaints about any dry boxes I've seen and this one is that 1) there isn't a way to re-roll the filament without opening the drybox (introducing more humidity) 2) there isn't a way to put the filament back through the tube when you go to use it again without opening the dry box... (again introducing more humidity).
I'm trying to come up with a way to have the rod that holds the spool come out one side with a crank on it, but there are numerous obstacles I haven't come up with solutions that I'm happy with yet.