When adding the extra batteries to the existing bank while camping, it works ok to have them as the "downstream battery." Although it is not ideal it still works.
In that set-up, you will find that the downstream set does not take as much of the load-- as seen on its loaded voltage, but after the load is removed, the voltage slowly recovers as they equalize.
So you do get the benefit of more AH available while camping, but not quite the same benefit as a balanced set-up if using the microwave/inverter for how far down the voltage gets with the load on. (if getting close to inverter alarm at 11v this matters)
Better than not having the extra batts though. It just takes time for the extra batts to share with the main set. You might not even notice the difference if you are not "instrumented" for all that, and are just a normal person going RVing :)
Once home and on Float, it helps to disconnect the extras from the main set and let the converter Float the main set of batts and use a separate floating charger on the extras. That way each set will float properly and one will not lose out on whatever sharing might happen with just the one converter on the upstream batteries.
