Mice love trailers. How they get in is open to speculation. More than that, they love to chew on things. Seal all cracks/openings you can find and, after that, two or three containers of d-Con usually takes care of the problem should one develop.
Flush out the holding tanks to make sure they are clean. Make sure they are well drained.
Leave the refer door(s) ajar to prevent any possibility of mildew or mold, at least until you are sure it is bone dry.
Remove any cans or bottles that could freeze and burst.
Happy Camping! ///// Richard D.
2006 4x4 Ford 250 SD / 2007 Flagstaff 827 FLS
One very patient wife and one furry child who travels with us. Forty-two years of trailering and camping, and I still have a blast.