I use a bunch of Relay Go devices for tracking my kids during ski season, so I figured I'll try to do a custom charging stand. 

I started by creating a basic rectangular shape, using rough measurements, and link it using rectangles. This v1 version actually worked pretty well by itself. 

However, I wanted to challenge myself and try to fit a curve at the bottom so the fit is snug - hence I did the v2 version =). I also optimized it by adding holes inside certain sections and the connector itself. 

I printed it with .20 w/ my Prusa MINI+. I tried printing it with 0.10mm, but it turned out worse :(. 0.20mm w/ 0.40mm nozzle turned out the best for me. 

The version I printed is really the v3 version, where I added my kids' initials just for kicks =)

Anyway, I uploaded a bunch of STL files so if you want to make your own custom X slots with initials you can do it easily using TinkerCad.