A platform trailer includes a load carrying main frame and an elongated loading deck supported by the main frame and defining a generally planar surface upon which cargo may be loaded. An elongated side rail is attached to at least one of the loading deck and the main frame so that the side rail is disposed along a longitudinal edge of the trailer. The side rail defines an upwardly opening channel extending along the longitudinal edge. The channel has a planar central portion substantially parallel to a plane defined by an upper horizontal surface of the loading deck and opposing side portions extending vertically upward from the central portion.