Big shout-out to Pete Schwamb, the Riley Link & Loop contributors. This project is an evolution of their awesome work and would’t have been possible without it.
The waterproof case consists of two parts (top and bottom), is sealed by a silicone seal and held in place by a rubber band. Feel free to print one yourself or have a look at Shapeways if you do not have access to a 3D printer.
Some very decent print result was achieved with the following setup
The main silicone seal is borrowed from AMP Superseal connector with 6 positions (Digikey Partnumber A106530-ND). Any rubber band with decent tension is good enough to hold to top and bottom of the case in place.
Inductive charging module
To add reliable inductive charging to the case make sure to use Adafruits Universal Qi Wireless Receiver Module. The flex PCB might be cut off (1mm) on the left side in order to fit the top-case. Connect the charging module to 'ALT PWR' on RileyLink side. Make sure to double check for ground and VCC. Any (cheap) QI certified charging basestation works fine to charge the battery. The red charging LED will turn off when the battery is fully charged.
The battery compartment can hold up to a 900mAh LiPo battery pack with a standard JST-PH connector (2mm pitch). Make sure there is enough space between the inductive charging module and the LiPo battery due to expansion while charging. Sucessfully tested with a LiPo battery 42mm x 34mm x 6mm.
Please make sure to test your case in a water condition before inserting the electronic components. Small pieces of paper added to the case compartments work fine to detect potential water leaks.
And please don't blow yourself up in the process. Have fun.