I had your exact same rig and lived in the woods. I was never able to keep them out. I tried so many things but nothing worked. In the winter I took everything out and stored it away from my home. After using mothballs in another rig I found that I detested the smell of moth balls so gave that up. I began using a bucket trap in the rig and this worked for killing them but not for keeping them out. I however never got anymore nests inside. I guess they were killed before they could set up housekeeping. They are disgusting and I now believe that the only good mouse is a dead one.