I see the balancing act amongst the batteries, but AFAIK, it doesn't matter between pos and neg for the load/charging wires, since it is their total that counts.
What makes it awkward is the Trimetric shunt. That adds a bit to the neg side, so you can't get it the same as the pos side anyway without scientific measurements. But that shouldn't matter since it is not between batteries, so you are allowed to have different neg and pos.
However, as a sinner, I have at times used the buss bars as a way to run wires from them to the batts so that the same wires are not only the load to battery wires, but also the paralleling wires.
This saves wire, but hopes that each leg takes half the amps. Now it gets very messy! :) Balance, shmalance!