The links between batts 2 and 3 will be eight feet long so there goes having all links the same :)
I chose dividing up the loads between big inverter loading on one bank and the rest on the other because it was easier to keep each bank properly looked after( no uneven charging or discharging among batts in a bank), and I was still taking advantage of having lots of battery
If you just have inverter-battery the battery does not need to be grounded to the frame. The bank doing the rest of the rig does need a frame ground to complete the neg path for several rig items that use the frame as neg.