an open top vessel containing bulk or liquid material comprising an inclined front wall , an inclined rear wall , and inclined opposite side walls . the walls of the vessel extend downwardly and inwardly from the upper ends thereof towards the lower ends thereof towards a discharge opening formed at the lower end of the vessel . a support frame is provided for supporting the vessel and includes at least a pair of horizontally spaced - apart , horizontally disposed support frame members which receive inverted u - shaped supports on the upper end of the vessel . the vessel is ideally suited for use as a hopper bottom in a hopper bottom trailer . the vessel is comprised of a fiber reinforced plastic material .