I wanted the freedom of not having to change anything when I plugged into 120. I found the ckt that feeds the gfi breaker plugs, that included the tv, kitchen, bathroom and the outlet under the storage and spliced the inverter/charger in to that wire where it exits the breaker panel. I also unplugged the 12 volt converter.
When plugged in to 120 volts, the inverter switches across the line passing the 120v and supplying charge voltage to the batteries, when disconnected from the 120 the inverter switches to inverter using the battery to supply 120 to all the plugs connected to the GFI ckt.
I run the fridge and the water heater on gas. with this setup I can't use the microwave, it's on a different breaker in the panel.