There is a full-time auxiliary power to the rear of the truck on every model year I've worked on. If you use this full-time auxiliary power to charge the trailer battery in parallel, it should even out with your truck battery and not draw down when idle/unoccupied. This being said, you would still be drawing on the truck battery when using the trailer interior lighting wired to the trailer battery with the truck off.
Is your concern keeping the truck battery isolated to prevent being unable to start your truck? You could get an isolation switch and install it inline with the auxiliary power to the rear of the vehicle, but that causes other issues with different trailer setups, I assume... Or you could put something on the trailer that isolates it when you want to manually isolate the trailer power supply from the truck.
You can wire in one of these to isolate the charging lead from the main truck system. The small leads would be switched power from a key on power lead and the large ones would be used to interrupt the charging lead. Key on, power to the trailer battery, and disconnected when the key is off. That way your trailer batteries handle your trailer usage without killing the truck.
I typed this hours ago, guess I forgot to hit the post button. I agree with the other guys, and here's my 2 cents.
I don't know the wiring of the 2017; but it is probably like the previous years.
In which the aux 12 volts wire in the trailer plug is connected to the trucks battery.
Normally this wire is hot when the key is off, so that the trailer has power.
If you add a battery to the trailer, the truck battery will discharge with the trailer battery.
You could tie in a battery illuminator, or just unplug the connector when you stop.
A forum community dedicated to all General Motors truck owners and enthusiasts. Come join the discussion about performance, lift kits, wheels, tires, modifications, troubleshooting, maintenance, and more!