I'm finishing an unfinished closet under the main stairs. I'll use it as a kitchen pantry/storage. I'm building a knee wall to limit the depth since it gets so narrow. Subfloors are red oak on pier and beam. I get a very cold draft during the winter when I stand in front of the staircase, so I want to insulate behind the knee wall. Can I just lay batting back there? Should I insulate and drywall the entire closet before putting the knee wall in place?