I printed mine out of Overture TPU at 100% infill. I'm not sure how stiff the TPU is as it's not written on the spool and I bought it a few years ago, but it's just a bit too flexible as is.  If you can print this with a stiffer TPU it'd be a bit more securely attached.  But it is fairly secure, and I'll know for sure how secure after it's tossed in my backpack 100 times.

You could probably print this out of plastic and slide it on from the side (with one controller removed) as well.  Up to you.

The top USB-C cutout was slightly off center when I printed mine, so I moved it 2mm to the left on the model uploaded.  If anyone does a print and it's still off, let me know and I'll adjust it again.