Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:5246210.
I wanted a way to charge the trackers, off the desk and without taking off the straps. Unlike a previous Vive tracker, there isn't a good way to "hold" onto the tracker if the bottom has something attached. So the USB port provides that mounting solution. The plastic here is just a guide to help me find the usb port. I imagine this could also work with magnetic connectors, I've tried to avoid them since I heard they burn out vr controllers sometimes.
As for the model I wanted something I could print without supports on a prusa mini. Though you might still want some brims if your bead adhesion isn't great. As for the USB, I just used hot glue. Held the tracker in position plugged in a USB and hot glued around it. Kind of messy but figured the hot glue would act as rudimentary suspension. So a misalignment of the usb and the holder, or the weight of the straps pulling on the trackers, the hot glue would take up some of the pressure.