Abstract: An improved sleeve pack assembly to be used to form a container comprises four vertical wall panels having hinged side flaps wherein the flaps and panels form doubled panel edge structures with securing edges along the flap edges. Four cornerposts hold the panels together and each comprises two generally perpendicular longitudinal channels which define a slot to receive the doubled edge structure and side flap of a panel. At least one channel wall includes a hooking edge, protruding inwardly of the slot, which abuts against the securing edge of the flap to lock the side flap and doubled edge structure into the cornerpost slots to hold the wall panels together into a sleeve pack assembly. In a collapsible embodiment of the sleeve pack, the longitudinal channels are in separate pieces which are hinged together to form a hingable cornerpost. The collapsible sleeve pack assembly further includes two opposing wall panels which are scored to be folded, and the sleeve pack assembly is collapsible.