Jeannie - Congratulations on your purchase. You likely are correct that the house battery does not get overcharged when plugged into 110 volt if the {store/in use} has disconnected the charging circuit to the battery. Normally no light will work in the house as they are all connected to the house battery and you have it disconnected.
Just thought I would share what I did about leveling the fridge. I drove to what looked like a level spot on a parking lot. Took my level and placed it on the top of the slightly open refrigerator door. You can swing it to get a reading on how level the fridge is side to side and front to back.
Move the motorhome if need be to another spot on the lot. When I felt good about how level the fridge was, I placed stick on levels on the driver door and on the face of the dash like these -

Now I just try leveling the motorhome in the parking area by looking at my levels.