I went into the default settings for the railing and under "Wall Types" there is a pull-down for the wall type. I had ignored that thinking it would not matter since I was defining the panels, newel posts, rails and rail style. The default for "Interior Railing" was defined as a layer of drywall on either side of fir studs. While I can change the materials and delete some of the layers, I cannot delete the Main Layer. So I made it the "Insulation Air Gap" as you suggested and it is no longer visible. Thank you for the work around!
JParch's post in How to remove phantom polylines at loft? was marked as the answer