I saw this simple solution of using an affordable shoe rack for filament storage. I found the shelf to be pretty wobbly once filament was loaded and designed these stabilizing braces to give me a little more confidence it's not going to come crashing down.

I tried a few levels using these spacers which made it even more unstable. With these stabilizers in place I was able to use the spacers scaled vertically 150% to give enough clearance to store most filament boxes.

There are many shelf designs that look the same. I bought this shelf.

In order for the braces to snap around the bars the material needs to be slightly flexible. I recommend PETG as it is both durable and slightly flexible. Do not use matte PETG. I tried it and it is too brittle - the clips for the bars snapped off.