Connect the "battery" negative terminal to the negative stud on the battery monitor shunt. Attach everything negative from... solar, truck alternator charging, all return loads from camper... to the aux side of the shunt.
The camper negative wiring is connected to the camper frame from a negative buss bar. As long as those grounds go back to the shunt then the shunt will see the return current back to the battery.
The shunt will tell the battery monitor what is going in and out (closes the circuit loop) from everything attached this way.
If you have anything bypassing the shunt and attached to the negative side of the battery directly then the battery monitor will never see this.
Picture the battery as a loop, positive out to load and returns as ground back to the battery. It takes both to complete the circuit.
So the ground from the battery should be already grounded to the camper frame at the breaker/fuses location by a buss bar. Also note that at the buss bar the power inverter has a wire that connects to it and then goes to the battery negative return. If your camper has standard factory wiring then you already have a attached wire from the camper frame to the battery wired properly, just attach that wire to the input side of the shunt as that is the only negative wire from the camper.
Love this explanation... thanks!