Here's a case for your Sandisk Extreme Portable USB-C SSD. I wanted a case that was a little bit of protection, without adding too much bulk. It has 2mm walls. I've tested with 25% infill and with 100%. Since it's so compact, I'd recommend 100%. There just isn't a ton of space to be concerned about infill.

I'll likely be designing a second case that houses the drive and the attachments to the drive(cable, adapter). 

This model uses 6mm x 3mm magnets. The magnet holes are set to 6.25mm, so they're a little loose, but stay in fine with some CA glue or super glue. Make sure to check your polarity before gluing. 

Here are the magnets I used:
https://a.co/d/hu8GvTp