To have the LiPo battery’s exposed underneath the longboard could damage them if something hit them. A strong chassis for the battery’s would protect them, as well as covering the cables from dirt.
The chassis is primary made out of 8mm polycarbonate, with a sheet of 1mm flexible PET cover.
The 8mm thick sides will hopefully take up the forces from any direct bumps.
CAD-files (Zipped Solidworks and DXF)
Cam Lock Screw
For locking the chassis to the board I used cam lock screws, the same that is often used in IKEA furniture.
The cam lock seems to come loose due to vibrations, so another solution might be needed.