I think the final product should be dipped in a barrel of epoxy, dried, and then put in the case and shipped. Master lock does this with their Bluetooth locks, and the locks are completely waterproof.
In fact, could the entire device be made out of a sort of super glue rubber mould?
The circuit board could be like the film you find on an old USB keyboard.
The case could be made out of one of the glues where it's sort of rubbery and doesn't break. It would also be color customizable. I want a dark green one!
It would be helpful for if you drop your phone, it just bounces a little. If you had a waterproof phone, you could play 'Father.IO - Tactical Ocean Explorers Beta' and everything would be fine! Maybe you should get the device rated for 10/15BAR. My watch is 20BAR.