A door system includes a flexible corrugated closure member guided between door open and closed positions in spaced apart opposed vertical and horizontal sets of guide tracks and further guided by transition guide wheels mounted on an enclosure frame for guiding the closure member between the sets of guide tracks. The transition guide wheels are supported for movement between working and non-working positions to facilitate storage or shipping the door system or an enclosure unit including the door system, as a substantially planar stack of wall, ceiling and floor members forming the enclosure.