Made this out of a plastic bottle after seeing a YouTube video (can't give credit unfortunately as I can't find it anymore).
You can make it into any shape that the bottle will fit around (and can't be much smaller than the bottle since it will only shrink so much).
I used a piece of wood as template, cut the top of the bottle, put it around the piece of wood and shrank it with a heat gun. I then cut off the excess and shaped the closing mechanism.
It took a few tries to get it right but I've since used the technique to make containers/protections for several objects and I'm very happy with the results!
If you want to try this, be aware that the tightest you shrink the bottle around the template, the hardest it will be getting it out! I suggest making the template in atleast 2 pieces, this helped me a lot. (In this example I first pulled out the small wooden tab with pliers, and once out the bigger one came out easily).
