The GP-RVC-30-MPPT has two battery outputs: BAT1 and BAT2. The solar controller will prioritize BAT1 at all times to ensure it is always charged as much as possible. After BAT1 has completed absorption charging excess power will be used to charge BAT2. The intention here is to maintain the house battery on an RV to be the highest state of charge possible and then top up the starter battery if needed.
The intended wiring for a motorized RV is shown below.
The detailed charging prioritization is shown in the flowchart below.