main Breaker Box

Most RV have DC lights but the appliances are what? AC or DC? Which is it?

Assuming you meant DC appliances like the propane heater and galley blower, the lack of power is likely due to low battery voltage. Evidently you only get DC power when you switch in the Aux battery. My guess is the main house battery has failed due to lack of charging, low electrolyte, or sulfation. Or a combination of the above. Many of the converters used on RV have a low battery disconnect. It is there to warn you when the main battery neds servicing and prevent damage due to excessive deep discharge. Without it you would simply continue to power the appliances from the power post external power not realizing the house battery had failed.

I'm not familiar with that particular model ( Bounder) but most RV have the main breaker box located to be accessible from the interior. Some models have a main DISCONNECT close to the actual battery. Look under built in seat bases or in a closet /cabinet close to the entrance door. One time I located a main breaker/disconnect right next to the entrance steps. The service tech could not figure out how to turn on the interior lights.

Have you confirmed there IS powers coming from the shore line? THe Bounder breakers are all on the panel down low by the Refrigerator I think. THe inverter is usually located under the dinette seat.