I have a 27.5 HT BHS, and a pet black squirrel. Previous comments are right on. Even thought every thing looks sealed, it ain't. Under the kitchen sink, take out the wall(?) toward the back - wow two large holes, staple 1/4 hardware screen over holes. The squirrel stored 80+ black walnut in wife's favorite pots in the drawers. Again under the kitchen sink toward the front - I filled in the top (built) up to seal the drawer area.
The furnace duct work and wiring is not sealed too good either (remove the grate and look). Now to the front storage - easy to climb over the gas tanks (tried to put some hardware screen under the tanks, almost worked). I finally extended the wall between the tanks and the tanks, by the way the landing gear drive goes through there.
Out of the 6 TT I've owned this is the first Swiss cheese. Yes, I did use the dryer sheets and other deterrents. By the way I removed the walnuts plugged the holes I could find - he brought in smaller nuts, acorns (80+). If you want to try the expanding foam, get the can the says rodent repellent also.