I was looking for a case to print for my wife for her Smok Novo X and a couple of tanks and could not find one anywhere. So I used my Einscan SE to scan in the insert from the box it came in and used those shapes to make the insert and then used a box maker to make the box to fit the insert.
For the external case Pet-G is suggested to allow the flexibility of the joints for the lid, most other plastics will not stand up to what is required. I used this openscad project to model it https://www.thingiverse.com/thing:384919
For the insert, I used TPU @5% infill to make it nice and flexible. This allows it to hold the tanks when you need to dump the vape into your hand.
You can print the whole thing out of pet-g without an insert but I haven't done that and the case holes are purposely sized a little short so they won't fall out when you turn the case upside down to drop out the vape. So I don't know the success of that.
If you want to play with the files, they are here, feel free to mod to your hearts content.
https://www.tinkercad.com/things/kP8MSz3VMbN
In the pictures, the white case is to show off the insert. The black on black is the way she carries it.
The author marked this model as their own original creation.