The IKEA SAMLA Boxes (22 l / 6 gallon) is the ideal storage solution for my needs. The profiled wall design makes it very stable. It can hold up to 5x 750g standard spools and I can put Silica gel inside. The IKEA SAMLA boxes should be available in many countries in the world.  
By mounting an installations tube in the box, I can feed the filament direct from the box to my printer. That's very convenient!  
My spool have all about 20 cm / 8 inch diameter but there is some space left to the wall, so 21.5 cm / 8.5 inch should also fit fine.
It is fast and easy to print. It is very easy to assemble. A drilling jig is also included.  
The STL files are for M4 screw and nuts, but as it is customizable you can configure it also for inch parts, other tube/pipe or boxes.  
I recommend also this things:
Spacer to hold the spools apart (I'm using simple_spacer_32x5.stl and simple_spacer_32x10.stl )
the Spool Adapter for perfect fitting of different spools
a Filament Clip
For sealing your boxes, you may find this…