You might want to talk with the folks at "ARM" (the Association of Railway Museums)
http://www.railwaymuseums.org 

I sounds like you are looking for a shelter (roof) that might keep them protected but also still provides access.  While it may or may not be helpful, I seem to remember seeing/reading an interesting technical leaflet that the ARM folks produced on how best to "encapsulate" (temporarily mothball) a railway car.

www.FireMuseumNetwork.org

We are working with another non-profit that runs the Atchison Rail Museum and are seeking some ideas, or how other places have already solved similar problems. 
 
The rail cars, including 1902 Steam Engine, several unique caboose designs, dining and other cars are in an open air setting and beginning to show deterioration - we know we have to do something soon otherwise we will begin to lose these pieces of our railroad heritage. 
 
Has anyone already taken on this problem - designed and built a cover structure to keep railroad cars out of the weather? 
Any advice on this or if you know places that have their rail cars covered that I could seek out information from would be great. 
Also any suggestions on someone who specializes in conserving railcars, old fire equipment, etc. 
 
Thanks in advance for your suggestions. 
 
Chris Taylor 
Executive Director 
Atchison County Historical Society 
P.O. Box 201 
200 S. 10th Street, Santa Fe Depot 
Atchison, KS 66002 
913-367-6238 
[log in to unmask] 
www.atchisonhistory.org 
 
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