Hi nano,
Welcome to FRF and Congrats on your new camping trailer.
When plugged into shore power(30 amp, 120 volts) everything should work, even with the battery disconnected.
Have you checked to see if you've got power to the Converter(Power Distribution Box)?
All of the 110 volt breakers in the ON position.
Is there power to the 12 volt fuses?
All About RV Converters