Take some time and look for any opening, large or small and fill it with this

Also build one or two buckets of death and place them outside the RV. You want to make rodents want to go where they smell food (peanut butter) instead of going into your unit.

The ones I built have tight snap on lids because I pour windshield washer fluid into the bottom (poisonous to wife's dogs) instead of plain water. That way it stays liquid all winter long.
Last winter I bagged more than 2 dozen mice. RIP varmints.