remaining open on one side so that moisture is not trapped and rust occurrence is greatly diminished the corrugations 22 shown in fig1 are placed in locations where the greatest stresses on the door have been found to occur during latching and during transit of a heavy load pressing against the doors from inside as will be discussed below the corrugations 22 of each door coact with the door edge structure to provide a door of high strength durability and structural integrity utilizing relatively thin sheet metal for the surface the perspective view of fig2 shows a portion of a door including a corner which may be the upper right corner of the door 11 although all other corners are similar the formed portion or 34 skin 34 23 is of light gauge metal but is greatly reinforced by the corrugations 22 and the edge structure the skin may be for example sheet steel of about 12 guage for a door of 44 inches by 90 inches at the side right edge of the door the sheet metal skin 23 is formed in generally right angular bends into a lip 24 with a recess involving several additional right angle bends not shown in fig2 lying just inside the lip onto the upper edge of the skin 23 of the same depth as.