I'd personally opt for the indoor storage, easier clean-up when bringing it out of hibernation and safe from whatever Mother Nature might dish out. As far as mouse proofing goes, I've been throwing Bounce dryer sheets in every nook and cranny while storing. Heard that rodents didn't like the smell and so far so good, no mice (which with saying that I probably just jinxed myself
) Plus don't get the musty smell that you sometimes do from the unit being closed up. Also we leave nothing in the trailer (no clothes, food, soap etc.).