One form of "weathering" that is rarely seen on plastic models, but very common on the prototype, is the denting and damage that the sheet metal undergoes over time. I have photos of a corrugated metal sided building (likely wood underneath) where the area of the freight doors is incredibly banged up, with the bottom edges of the sheathing curling up and deep dents around each freight door. In other words it does not have that clean flat regularity of the molded kit parts.
One way to approximate that is thin foil cut to the size of the metal sheets modeled on the kit, pressed into the corrugations of the kit using perhaps a dried up ball point pen (an old E.L. Moore trick) and cemented over the stiff plastic sheet. Moore also made corrugated metal out of stiff bond paper pressed into corrugated metal or plastic using that dried ball point pen. He might have then stiffened the paper using shellac. A large sheet could be done at one time, and then cut into the appropriate sized pieces. The whole building should not look dented and dinged but at strategic points it can be very effective.
Dave Nelson
