Abstract: A support bracket kit, particularly for use with vehicles having a cargo storage area including sidewalls, a bottom wall, and a pair of wheel wells. The kit is comprised of at least one cross-beam for disposition generally between upper portions of the wheel wells. A plurality of corner support brackets are disposed between the sidewalls and the floor in each corner of the cargo storage area. The support bracket kit allows a cargo box of a pick-up truck to be adapted to receive, for example, four-by-eight-foot sheets of plywood or drywall which are supported above the wheel wells by the support bracket kit.