Did that a couple years ago. The 5er is now wired like a typical cruising boat. No more converter charger. Installed a pure sine wave 2000W inverter charger & a single 4D Lifeline AGM battery. The 4D battery has about the same AHs as a pair of 6Vs but without all of the addional linking cable.
With the inverter turned on ALL 110AC circuits are live so to prevent killing the battery in only a couple of hours the power hungry AC draws, water heater, fridge, microwave, air, are turned off at the circuit breaker panel. This leaves all outlets live.