Can be printed on a 6x6x6" machine. Just orient the two battery halves such that the tapered end is on the platform and diagonal so that it fits within the build envelope.
The VESC case can be printed upside-down so that minimal supports are necessary.
Sealing and fastening
Not pictured: Weather stripping will be applied to the board in the shape of each case. Wood screws will fasten each case down and press the edge of each case into the weather stripping to form a watertight seal. Each case's bottom is curved to a radius of 17.25" to match the curvature of the board (I've tested this on two types, and it seems to match both well).
A hole is drilled under each enclosure, and a channel made using a router. 10AWG wire connects the battery case to the VESC case. Power is connected using a simple shorting jumper to connectors on the outside of the battery case.
Charging is done using a high-current hobby lipo charger and an externally exposed balance connector.
Translucent view to reveal VESC configuration inside.
The two halves of the battery enclosure shown as assembled.