X2 on the Blue Sea SI-ACR Automatic Charging Relay setup. It certainly appears to parallel the auxiliary batteries during charging, and isolates them when charging has stopped and after auxiliary battery voltage has fallen.
It does not appear however in my case to keep the parasitic Truck system loads from running down the Truck start battery. If I let my Ford truck sit for a couple of weeks the truck start battery starts loosing it charge. I suspect using the manual over-ride of the SI-ACR setup would rejuvenate my truck start battery allowing me to start the engine...
This would be a great feature to have for me to supplement my Ham radio operations from my truck setup...
This is my proposed setup using the Blue Sea SI ACR setup... My only untested fear is going to be will this extra load of the auxiliary batteries overload my standard OEM Truck Alternator system.

Love your TC setup and towing the Jeep.
Roy Ken