I have mine from.... an unused Basic cartridge.
The Premium version has the exact dimensions, I only had to work a little slot on the joint of the two halves for the opening of the sd-card bay.
I still have unused the Micro-SD bay, but I've planned to put in it the permanent files as it is blocked by the case and I don't want to open a big hole to access it.
If some day a good option is offered I will re-assemble the Basic cartridge. I don't like the finish of the actual 3-d printing technology...