Don, Masonite is a good idea.
John, I already laid track on the shelf parts pictured, and installed copious scenery.
Dave, the shelf system is attached to the wall studs, with cantilevered 2x4s every 8 feet. It's part of the wall and very strong
Tom, an elderly friend, who is a carpenter, helped me build this. You're photos reveal masterful wood-working. I am afraid I don't possess near that amount of talent. I am in Honey Brook, Chester County, Amish country. My e-mail is: Paulefudd@hotmail.com
Funny thing about planning layouts... we always end up wanting to make them bigger. In my case, I only need 3-4" to give a nicer foreground.