I'm doing some work on a doublewide mobile home. I am replacing windows with new construction vinyl. They have a nailing fin, and a J channel for later vinyl siding. I plan to first cover the exterior of the doublewide with 1/2" styrofoam panels.

To make things fit I want the styrofoam panel to go to the very edge of the rough window opening. Then I want to put the window nailing fin over the styrofoam. After shimming the window I'll nail through the fin, styrofoam, existing siding, and on into the 2x4 framing.

The foregoing process will allow the vinyl siding to evenly fit. My only concern is the stability of the styrofoam around the window opening.

Manufacturers don't recommend nailing the fin extremely tight. But, I wonder if the styrofoam might begin to deteriorate around the window's edge. It will be covered by vinyl siding and the fin itself.

Do contractors doing new houses run styrofoam panels to the window's rough opening and install new windows like I just mentioned? If not, how do they do it? Comments? ideas? Thanks, Gene