Me and my brother was quite active on efoil.builders some years ago, building two regular e-foils. Now we are building wearable foil assists for ourself, with two somewhat different approaches.
One Pack raft (primary path) approach – using a Aluminium or Stainless frame glued to waterproof fabric with a zipper or just folding it to make it waterproof.
One more conservative approach (backup) using a off the shelf waterproof box.
ESC: flipsky 75200 Pro
Motor: Flipsky 6834 w. alu prop
Foil: Gong curve H XL and Axxis 1010 with 70-80cm mast
Power cord: Polyurethan 3G2.5mm2 or 3G4.0mm2 Custom coiled
Off shelf box: B&W Type 500
Battery configuration: 12s3p 21700 Molicel 42A or equivalent
Busbars: Custom from Wellgo Battery Parts
Controller: Possibly Wired, TBD
Cable glands: Likely customized - will be shared once design is ready
Harness: 3D printed TPU
We are found of illustrations, so we will just tell the story for each image as we move along. We have started prototyping and ordered some materials, hopefully will have something functional over the summer. As our previous builds, we will share 3D files and drawings of everything when we have something that works 
Here is the Packraft approach, Its a metal “backbone” made of sheet metal and Waterproof fabric (Packraft fabric and/or dry suit fabric). The fabric is glued onto the sheet metal then made waterproof with a zipper or just folding it over on itself (like regular waterproof bags). The main idea here is that the metal backbone will act as a large heatsink and dissipate heat the battery as well as the ESC. With plenty of room for wiring and perhaps some refreshments
etc.
Here is the off the shelf box approach. Its similar to several builds we have seen here on foil zone. Heatsink for the ESC is milled through the side, the green part will be milled in aluminium and bolted to an external heatsink, clamping the cutout, preferably, waterproof. the box is only 500g and can just barly fit the ESC and the battery. Which we think is nice for waist mounting. The box also has these external fins, that will be nice to protect the Cable glands.
Our Battery will be 12s3p 6x6 21700 cells. We ordered 5x custom copper busbars with pre mounted nicklecopper weld strips from a shop at aliexpress - they look great! For next order we will move the balancing wire attachment as shown with the red dot, to prevent the battery from being wider from the balancing tab. We ordered a K-weld with a car battery, and started playing with welding. Having almost zero experience with battery welding, we thought we found a decent setting of 45J. At least Gemeni told it was approporatly dialed in.
At the day of welding the first pack something went wrong
After welding all the cells at 45J we found that at least 3 cells was punctured and leaking. It most definitively was user error, most likely too much force on the electrodes, incorrect/different calibration or different voltage on the battery (if that matters?). The battery was charged overnight, and the calibration was done holding the electrodes slightly different the next morning. In hindsight the welding should have been done immediately after doing the test welds. If anyone have some good tips here that would be appreciated. We are considering making a spring loaded mechanism of some sort, or weld under a microscope to make it more controlled. In any event - we have many more cells so we will just start over, and implement some improvements observed in the first build.
For balancing the battery our original thought was to have a charge only BMS inside the battery. To save weight and pack-build time we will make/get a balancing charger for 12s. Using a gold plated amphenol vga (15pin) connector as the balancing connector (+ temp sensor). The current idea is to just take the daly smart BMS and permanently attached to the charger and use it that way - with a customized connector to prevent improper connection sequence.
Cheers