One thing I forgot to remove last year was shampoo and body wash that I had stored under the bathroom sink. It "exploded" when it froze, so when it thawed, left a nice mess to clean up in the Spring. I remembered the stuff in the medicine cabinet, just not down under.
Our trailer is parked outside at our house, albeit on some packed down road base vs dirt or grass. We don't remove much other than anything liquid and of course food items. We've never had a mouse problem, but we also have dogs that run around in the yard that probably keep any mice away.
Also, we found a mobile tech that will come winterize it. It's $20 more than at the dealer but he can usually come out within the week, and it saves us the trip to/from the dealer.