We had the same problem with mice in Colorado. I had read that steel wool at the openings would work. The only opening I could find was in the rear bumper storage where the power cord, ect. enter the trailer. Stuffed the steel wool around it and have not had a mouse since. Either fixed it or we haven't been where mice live.
'99 25' Safari
2 Honda 2000i generators
'08 Chevy Duramax
'01 Yamaha Raptor ATV
'07 Yamaha Rhino ATV
2 burgler alarms: Rotweiller and Shepherd
"If you step down to get in, you have to step up to get out"