[Richard]

If you are driving without the genset on, isn't the alternator charging both battery banks? I thought this is what the battery isolator allows.

That is exactly what the isolator does, almost all mohos today have that setup. If an owner is diligent about house battery charge, and knows not to try to recharge a deeply discharged house bank with the alternator, then no harm no foul. The problem arises in two situations. One the house bank is depleted because the coach has boondocked and the owner having been told the engine will charge the house batteries, cranks up and drives away. This will KILL your alternator eventually, unless you have one of the oil cooled 50DN jobs. The second is the conversion to lithium for the house bank. The lithiums will accept amperage at an insane rate resulting in dead alternator.

There is no criticism of what you are doing. I put my opinion out there because there are many others reading the thread, and they may not have the experience and diligence that you do.

What inverter and control panel do you have? We may be able to tweak some of the charge settings to keep this from happening.