Holley Terminator X dry box. Over the years we have seen a few Holley Terminator X ECU's get damaged from pressure washing or heavy rains. We recommend mounting the ECU with the connectors pointing down and under a seat or foot stand, but even then water can damage an ECU. These are UL rated...
waterthunderparts.com
Other than I/O on the sub harnesses for things not needed, I don't think there's anything that runs to the engine that I wouldn't use. The ECU side I/Os that are unused can be easily tucked away.
The harness is well made. If you're super anal about having too much wire for some items and having to zip tie it out of the way, I can see wanting something custom.