Summary

Cradle for a Button+ module.
See https://button.plus/ for more info on Button+.

The cradle reuses the backplate that is included with the Button+ Base for rigidity.
You can easily squeeze the buttons between the back and front of the base, since only the middle portion extends to the back.
And lastly, it can house the 3.3VDC supply.

In the back there's an opening where I mounted a strain relief (SR-F41, see attachment). But you can adjust it with for example a cable gland or whatever is available for you. The Freecad files are included.

I had it printed in PLA, which printed very nicely, except for the top part of the strain relief opening. But, since the strain relief is placed over there anyway, you don't see that and I don't really care.
Of course, it is better to print it in black instead of white.