I took the really cool design from kpawel and TheTimetraveler then modified it for my purposes.
The main idea was that the square holes have a 27% wider opening surface without letting the round particles fall through any easier (the holes are still 1.5mm wide). Also a sphere and a square hole can never form a seal unlike a sphere and a circular hole. Furthermore I put more holes of them in the same area.
All three measures should improve circulation of air and boost effectiveness.
As a side effect it prints faster and with less material.
The above ideas and original items were great so i used them to make what I consider to be the perfect Silica container. First off I store all my filament in good old fashioned great value gallon size Ziploc bags which fit perfectly, I am sure vacuum bags are better but I just have not seen the need. I just suck as much air out as i can before sealing the bag and with one of these beauties inside it takes care of the rest.
So I wanted a container that would fit totally inside the hole in the middle of the filament spool so it would take up no additional space inside the bag so they would fit on the shelf the same. Also by giving it a couple of mm of space around it the container should work just as well in a vacuum bag if you prefer.
Also if your the type who uses dry boxes you can just set these up in the corners of your box and your golden.
Once you have the container printed hop over to Amazon and buy 3mm Silica Gel (rechargeable will be cheaper in the long run) Here is my recommendation.
Then while your on Amazon pick up These Hygrometers which will fit into your container perfectly. In my experience they work well, they tell temp as well (if that matters to you), the battery lasts a long time, and most importantly they are cheap enough that you don't have to sell a kidney to put one in each spool if you wish.
That's it, now you can cheaply store your spools for the long haul without spending a ton of money and all you need to do it check from time to time to see if the moisture level is rising and if so simply take out your container and recharge your silica and put it back in.
These are the settings I used but you can adjust as you wish. I would suggest keeping "Supports from Build Plate" on but not the rest of the supports on the container and no supports on the lid. This will give you supports to remove in the area that will be hidden by the Hygrometer but the rest of the supports were not necessary for a good print.