We have a 2001 M211, no slides. When we bought it used, it had signs of mice and we eventually found their nesting area, over the cab. I spent a lot of time on a creeper under the vehicle doing thorough mouse proofing. The place I'm pretty sure they were getting in was where the cab meets the coach on each side underneath behind the cab doors. They travelled from there, up behind the panels where the speakers are mounted into the overhead. I jammed those areas and a few other candidate areas I found with stainless steel wool. Haven't had any since.