Assembling blow molded parts to form cantilevered structures incorporating a joint among three blow molded parts. A joint incorporates connector components from each part. One part comprises a cantilever, and has a tab with a through hole disposed substantially at the fixed end. The other two parts are assembled using a barbed post-and-hole joint, such that the post is inserted through the hole in the tab. The tab acts in tension at an angle to oppose the moment and shear generated by the weight of the cantilever. Other aspects of the invention include an additional dovetail joint connecting the cantilever part and the other part or parts, The dovetail joint may be blind, and may contribute to supporting the weight of, as well as opposing the moment and shear.