Is that 150ft shore power cable providing you 30Amp 240VAC power? I assume so, if you are seeing 120V on both legs on the Aladdin screen.
That's a long cable. I use a 100ft cable but only 20A 120VAC power. In the Inverter settings you should set "Shore Power" to the "circuit breaker size of the shore power source" (i.e. In my case it is set to 20A) that is to prevent the shore power circuit breaker from tripping when there is a high load in the coach and the battery charger is charging on high.
It sounds like your House batteries went dead. I suspect when the shore power circuit breaker tripped, you had the Inverter turned on, so the batteries started providing power for your electric heater (being converted to 120V via the Inverter) until the batteries died.
When you are in storage, and connected to 120V/240V shore power, you can turn the Invertor Off, the Inverter's battery charger will continue to charge the batteries.
On my '05 the transfer switch is mounted on the upper back wall of the basement compartment between the frame rails, in the last compartment. Of course, your location may vary.
This is what it looks like:
Now that your shore power is working again, can you get the Aladdin to show voltage status again? Possibly you need to get your batteries up to 12V first. Also, when you're checking the battery voltage with your meter, be sure to note that the House batteries are 6V, so you need to check from pos to neg term across the two batteries in series to read 12V.