The AUX battery is currently running my ARB fridge/freezer inside the cab. You're right about how tedious it is to feed wire through the rubber boot in the firewall. I ended up using a shortened wire hanger to feed through the boot and tied the end of the cable to it. That worked great.
It will soon be running a switch box inside the truck cap to control three sets of lights, USB ports and an Anderson Powerpole connection.
Thanks again.