Abstract: A removable, replaceable and interchangeable trailer side panel assembly comprises a substantially rectangular panel body formed of a foamed plastic core having a layer of a plastic containing film adhered to each of the major surfaces thereof, and a rigid framing member secured to at least two opposing edges of the panel body. The side panel assemblies in accordance with the invention may be combined to form a flat bed trailer side panel container assembly. The side panels of the invention retain their dimensional stability, are practically maintenance free, last considerably longer and are significantly lighter than the replaceable side panels used previously.