A palletized shipping container (10) for bulk handling of liquids and fluent materials has a collapsible inner bag (30) enclosed in a flexible outer liner/bag (11) having rigid stiffener panels (20) in pocketed sides. The inner bag has a bung at its top end for filling or discharge and a valve fitment (50) near the bottom for receiving a discharge valve. Tape tabs (34, 19) at upper ends of the inner bag and outer liner/bag attach to the top panel and/or stiffener panels to maintain the bags in an erect uncollapsed configuration. The stiffener panels prevent bulging of the inner bag and provide vertical support, but their lateral sides are spaced apart and form non-structural “floating corners” to maximize volume, minimize shock, vibration and abrasive forces on the inner bag, yet maintain impact and compression strength meeting international certification standards. The bung is disposed beneath the top panel after filling the bag to prevent access and provide a tamper resistant assembly.