I would like to restate an obvious truth that some people have missed. In today's trailers you CANNOT "run it" on the battery. Sorry folks but it just doesn't work.
And, as far as those who don't want to use up their propane I think they are missing a big point. The fridge uses what is equivalent to a pilot light when in propane mode. If you want to save propane, don't use your furnace or hot water heater. These really eat up the propane, not so much with the fridge.
You are going to love your new trailer. Set the thing to automatic and don't worry. If you are plugged in it will change over. Once you unplug it will turn back to propane. I hit a button and the furnace comes on, I hit another button and the hot water comes on, the fridge runs all by itself. It is magic I tell you.