If you every wondered where mice get into your Airstream or Argosy, here are some holes I found in the 22' 1975 Argosy I am re doing now. Oh, they were nicely covered by shag carpet. But they are typical of the way pipes go through the floor on most every AS or Argosy I have owned. The third photo shows the heat duct to keep the holding tank warm. 2" pipe, 4" hole. I removed all the ductwork in this rig, and have one direct heat outlet. I covered up the mouse hole.
I use metal plates, steel wool or expanding foam to fill them up and that usually, but not always, takes care of the problem.