The goal was a cleanly installed water injection tank and pump system with a sizeable capacity that's easy to refill.
Tank modification to mount the pump and the float switch. This allowed the installation as a single unit and, given the extremely tight spaces involved, I didn't see a better way that still allowed ease of maintenance and the shortest possible plumbing.
Vehicles equipped with parking sensors would have additional electronics in this corner of the trunk, but since I don't this became the perfect place. Mounting involved heavy modification of the supporting plastic brace installed from the factory.
Carpet trim for the custom look.