I didn't read the whole thread carefully so I may have missed the point but in the case of the dual VMs staying on - in this case 'a ground isn't just a ground'. Since the VMs are both connected directly to the HOT terminals of both batteries, we're switching the ground side of the VMs to turn them OFF. In other words, we have to be able to switch the ground side off and that's what the relay is used for - key off, relay off, ground off, VMs off.