An apparatus (30) for forming a flattened seating area from a gabled bottom of a carton. The apparatus includes a cup (50) having a recess that conforms to the bottom cross-section of the gabled bottom. The cup (50) has an inlet (120) in fluid communication with an underpressure source. An anvil (145) is disposed within the cup recess (50) for forming the carton when the carton bottom and anvil (145) are driven together by, for example, the underpressure in the cup (50).
