Custimizable TUSH bracket (sized for Rubbermaid 21 cup filament storage)

I've been working on building a Rubbermaid filament storage system, and I was looking to improve a bit on [Jimbo70's system](https://www.thingiverse.com/thing:2769588). I printed the [TUSH remix](https://www.thingiverse.com/thing:2521463) but I found that (1) the brackets were too long and (2) they didn't quite fit the spool holders I had printed. I started to tweak my own and then realized that the ability to fine tune with a customizer might be helpful for many.
This lets you control the widt