Welcome Dan!
It sounds like the relay that switches your 12 volt interior power from that produced by your converter back to getting it straight from the battery is sticking.
Has your m/h been sitting parked for very long?
When I first bought mine I had a similar problem, but it didn't happen every time. To solve it I hooked the shore power line up to an extension cord plugged into a digital timer set to go on and off every hour. The constant 'exercising' of the relay cured it sometime during the week it was hooked up that way. It's never happened since.