be mounted in the notches 170 and or along the lower edges of the platform 39 s sidewalls and end walls to further reduce the risk of slippage during use in still further embodiments separate engagement features such as fasteners could be used to secure the platform sidewall or endwall in a notch with a desired placement and or orientation examples of such engagement features include pegs or gear teeth extending upward within notches 170 below the height of the upper plane of top section 131 which engage corresponding openings or gearing on the lower edges of the platform fig1 shows another embodiment of a generally rectangular support element 180 for use with platform 112 and having an upper portion 182 and a lower portion 184 as illustrated the support element 180 includes a closed center with two perpendicularly opposed notches 190 and 192 the profile of the notches 190 and 192 may be sized to accommodate different lower surfaces of a platform 112 or to allow support element 180 to be used to support different sizes or models of platforms for example notch 190 may be correspond to the profile of the lower edge of endwalls 125 of platform 112 thereby allowing platform 112 to be supported in a lengthwise angled arrangement similar to that shown in fig8 amp 9 likewise notch.