Abstract: A cargo bin formed of a medial cargo module having opposing open ends formed to securely engage an extension member to extend the length of the bin, or an end wall, for use when a non-extended bin is required. A unique engagement mechanism is provided for securely affixing the extension member or end wall to the medial cargo module, wherein there is provided a cradle formed to receive an engagement rod, the engagement mechanism formed to securely guide the components together so as to align engagement apertures associated with the side edges of the units, which engagement apertures, when aligned, are secured via retention pins or the like.