I usually take one of my wifes worn out nylons, put some mothballs inside them, then hang them under the motor cover. Keeps the rodents out, and it’s easy to dispose of in the spring. I use the same thing to hang inside closed covers in the boat. Then I put dryer sheets in on top of it all.
I have had mice absolutely destroy a popup camper. There was about a 3′ hole in the roof from the little pests.
Dragon ‘Em In