Most Inverters have a low voltage shutoff. I think you need to simplify and streamline things. One bank, one inverter supplying multiple 120v loads, and multiple charging sources. One season of boondocking should pay for everything.
The kill-a-watt keeps track of how many Kw Hours are consumed, as long as it remains plugged in. In a warm environment (80+F), with the freezer empty, get the freezer cold, THEN plug it in to the kill-a-watt, and let it run for a few days. Divide by 3 for the daily average, adding a little to allow for opening the door occasionally. Then you'll know for sure. And when full of frozen food, it should run even less.