Dash lights should be on the chassis battery so that suggests a second problem.
My first suspicion for the house battery would be the battery isolator is not working or perhaps you have a tripped CB on the wire to the battery. You could have a corroded connection inside a lug that is clamped onto the wire. Di-electric grease won't help there. With the engine running, headlights on and a voltmeter you should see 13.2V+ at the isolator input and both outputs and then test the voltage back to the battery. Shore and solar off for this testing.