@RJT posted:Aegis21 Homosote will hold screws better than foam. I covered my entire layout with homosite.
I agree with Rick. Some places I covered the whole area with Homasote, and other areas (mostly grades) I cut it to be an inch or two wider than the track. Forum member Ken Hoganson (Ken-Oscale) recommended using a wide drywall anchor in styrofoam then sinking the track screws into it. I used it on my 2" foam board for my old Christmas layout. That method was okay for a lightweight temporary layout, but for a permanent layout, I prefer Homasote by far.