I would think about small
Breaker Panel. Put an automatic transfer switch between the generator, and shore power inlet (to automate things), then the small breaker panel, with a 30 amp breaker feeding a second automatic transfer switch (with the inverter feeding the other side), powering your main breaker panel.
Move your AC, water heater, and converter to the (new) sub-panel.
Theory is on generator, or shore power (automatically switch between if available) you have ac, electric water heater, battery charger (converter), and the entire rest of the trailer. Lacking shore / generator power it load sheds the big stuff, and powers the entire rest of the trailer off the inverter.
You said you already had a automatic transfer switch, if it is in good shape, use it for the inverter input. You can plug the shore power plug into the generator if you want to pinch pennies.