illustrated in the figures there is provided a pair of parallel preferably 34 u 34 shaped channel members 40 and 42 rigidly attached along each side wall 16 and 18 respectively for slidably accomodating metal plate 34 thereinto allowing the placement and the removal of metal plate easily likewise there is provided a second pair of parallel 34 u 34 shaped channels 44 and 46 for accomodating metal plate member 36 in a likewise fashion once slid into position plate members 34 and 36 serve to divide overall container space 32 in the three spaces 32a 32b and 32c as discussed earlier in the preferred embodiment 34 u 34 shaped channels 40 42 44 46 are maintained in rigid connection to side walls 16 and 18 through welding bolting or the like most importantly being of such thickness and rigidity to rigidly support plate members 34 and 36 when they are needed to bear the weight loads of sand gravel cement or the like also although only two partitions 34 and 36 are illustrated in the preferred embodiment if one wished one could place a number of partition members having a likewise equal number of rear door members in order to operate as.