Update 2-16-2017: I have added an alternate design for the PTFE port to support 4 mm tubing. The new design uses a cap and a clip rather than an integrate cap port. It uses the same spool cradles. I did this redesign so that I could better support CoreXY and HyperCube printers with a port mounted low on the container. You will need a 10mm PTFE connector and will need to drill a hole to mount the connector. See the second photo.

I had problems with moisture getting into my filament and causing little pops on the side of my prints. I realized when the problem did not occur with a fresh spool of filament that my filament was absorbing moisture. This Airtight Filament Canister solves the moisture problem and provides convenient storage. It includes a cradle for the filament spool to move freely based on six 608 bearings. The filament is fed through an airtight connection using 1/4" PTFE tubing. I used larger tubing to avoid introducing drag on the feed of the filament. The canister is completely airtight except for the small hole in the end of the tubing where the filament exits. Once I'm done printing, I cut the filament off and plug the end of the tubing in the spare dummy port which seals the end of the tube. The dummy port does not enter the canister. It is a blind cap integral to the filament port. I chose to install the filament port on top because I run with it on my desk. If you would like your canister on a shelf above the printer, you may install the filament port on the side of the canister, even near the bottom. It can be glued into any 1/2" hole on the canister.

There are two versions of the cradle, one for narrower spools and one for wider spools. This canister will not handle spools over 78mm wide. Its a limitation of the Rubbermaid Canister. I chose two cradles because an adjustable cradle is harder to print and did not look as nice and simple as the one piece design. The Rubbermaid container is a 21 cup size and can be bought at Amazon.com for $12.
http://www.amazon.com/Rubbermaid-1840750-Modular-Storage-Container/dp/B00BEUDWIC/ref=sr_1_2?ie=UTF8&qid=1455209151&sr=8-2&keywords=Rubbermaid+21+cup

The bearings can be bought anywhere including a skate shop and should cost around 75 cents each. The 1/4" PTFE is available from Home Depot. There is no other hardware for this design.

Update1: I have been using my new canister quite a bit this week and noticed that it feeds better if you face the canister and PTFE so it follows the natural curve of the filament coming off of the spool. (Makes sense doesn't it :)
Update2: I printed another one of these setups and I am keeping my favorite filaments in these canisters. It is much easier to hook them to my printer and it is easier to seal them off rather than zip lock bags which is how I store my other spools of filament. This canister has eliminated any problems I was having with moisture getting into my filament.
Update3: I received a spool of Hatchbox filament that did not fit the smaller of the two cradle designs so I narrowed the smaller one by 10mm. Between the two cradles, this canister design will support spools from 56mm through 80mm wide.
Update 4: I added a filament guide that mounts on the printer and receives the 0.25" PTFE guiding it to the middle of the top of the printer. This makes it easy to connect and to swap out canisters. You clip the filament, unplug the tubing and plug in another canister.