used in the art may also be employed for the boards 14 the frame 12 is constructed from any suitable material such as steel in one embodiment the frame 12 may comprises a third longitudinal member comprising a mid rail 32 which is connected at each end to the midpoint of each end member 18 in an orientation that is substantially parallel to each longitudinal member 20 in one embodiment the mid rail 32 is an i beam thereby having slots 34 facing the longitudinal members 20 the boards 14 insert into and are retained by the slots 34 on the mid rail 32 a plurality of cross beam straps 36 are arranged in an orientation that is substantially parallel to the opposing end members 18 each cross beam strap 36 comprises a flat metal bar and is connected at one end to the mid rail 32 and at the other end to a longitudinal member 20 in the prior art cross beam straps are used but are butt welded to the longitudinal members and the mid rail such that it is disposed on top of the boards 14 and flush with the longitudinal members and mid rail in the present invention the applicant has found that by modifying the installation of the cross beam strap significantly better results may be obtained as shown in fig2 a transverse groove is cut into the boards 14 having a depth approximately equal to the thickness of the cross beam strap 36 the strap 36 is lengthened slightly such that the ends overlap and slide under the longitudinal member channel on one side and within the mid.