Along the lines of the previous post, you could use the slats as KEB suggested and then rig it like an Oleo or Roll drop.  Not metal, but cheaper and easier to construct.  Try this article for how to make an Oleo  http://www.studio-productions-inc.com/white_papers/wp_oleo_olio_rolldrop.html (the article directions were compiled from Greenroom sources and some internet research, because I kept getting questions from customers on how to solve no-fly space problems)

Also building on what KEB suggested with the 1x4's you could drill through the 1x4 edges (so 4" drilled hole in each end) and string cable through that to substitute for fancy carpentry and if you wanted you could go to a tack shop to find the type of channel that horse doors are hung on to be the side track.  This steel channel is in cross-section like a squared off 'C' and is also used as theater curtain track.