An idea i did in my 5th wheel was I just removed the black wire from the breaker and ran it thru a standard light switch then back to the breaker. When running on inverter I just shut the switch off. The only issue i ever had was forgetting to turn it on ! I had planned to change the switch to a lighted one so i knew it was on, but since replaced the camper...well moved out of it so to speak.
Installed my ATS just after the twist lock in the side of the camper. This allowed all circuits to be live. I was worried about the microwave and coffee maker but my inverter has a shutdown for over current so if she accidentally thinks she can use it it shuts down.