I'm loathe to jump in here as I don't know much about inverters. but I did want to share how ours is set up in case it helps to consider another alternative. A friend gave us a Xantrex inverter. Not wanting a free inverter to cost us an arm and a leg, we went through several months of researching how to install it and ultimately chose to spend an arm and a leg to have it professionally installed. After much discussion with the installer, we chose to have the inverter wired to only two of the six switches on our AC panel, the port and starboard outlets. It does NOT power the hot water heater, the battery charger (there is a separate charger for the starting batteries, the house batteries are charged by the inverter) the refrigerator (gets DC power if no shore power) or the range. If we need any of those other things while away from shore power, we have a generator.
The invertor has a control panel where we can turn off and on the charging and inverting functions and select "power share" to tell the unit how much of the incoming power it can use for charging. That is handy to limit how much power the xantrex is using so the generator does not overload and trip if we are also using other power sucking items.
So if we are leaving the slip and about to turn off shore power, we make sure the inverter is "on". this does not mean it is inverting, just that it is ready to invert if shore power is removed. Then when we do turn off the shore power, the inverter automatically takes over. If we have shore power on and we do not want the inverter to take over if the power goes out for some reason, we just make sure the inverter is "off". The inverter powers the two switches for outlets regardless of what the selector switch is set to (generator, off, shore power). now say the switch is on generator and the inverter is "on". If the generator is on and providing power, the inverter does NOT provide power, the charger will come on and charge as long as power is coming in. Instantaneously when we turn off the generator, the inverter takes back over and powers those two switches. If we left any other switches on when we powered down, they would lose power. they are not connected to the inverter.
I hope that makes some modicum of sense. I cannot explain how the wiring was done since we did not do it.
I have to tell you though, they did make one mistake and it was a pretty big one. We went out for a multi day trip shortly after we had this done and were having power issues on the 12 volt side. we were running the generator to charge the house batteries but after a couple of days our lights were dimming--the battery monitor looked like we should be ok and the batteries seemed to be charging up fine when we ran the generator. When we went to leave we could barely start the motors, we had to turn on the generator and turn on the separate charger for the starting batteries for a bit. The pros had wired the house panel to the starting batteries and only the inverter was wired to the house batteries!!
oopsies.