It wouldn't let me link multiple remix sources, so also based on multiboard.
https://www.multiboard.io/

Use with M4 bolts/nuts and your choice of Multiboard screw mounts. The rack perfectly fits an 8x panel front to back. 

2 panels can be mounted on the 1u if they fall close to the middle of a u, but a 3u gives much more flexibility.

I thought about designing it for use with heat-set inserts, but thought that using nuts gave more flexibility and reduced the complexity.

I've include the f3d file incase you need something different. You can change how many u by changing the parameter.