Collapsible reusable watertight carrying cases are provided in sizes varying from small containers without wheels to large sealable container bins on wheels, to provide large quantities of water or other supplies and cargo. The cases are assembled or disassembled from a joined flat space-saving configuration to a functioning case and vice-versa. The sides of the cases are erected progressively by hand by interlocking self sealing reciprocating channel and channel engaging members elements at the corners. The panels also disassemble progressively by being manually pulled apart. Optional foldable locking latches provide stability and aesthetics to the carrying case. When folded into a flat storage or shipping configuration, the panels stay together, resisting unfolding by virtue of snaps which are either molded into the panels or bonded to them. The carrying cases are resistant to water, dirt, bacteria, molds, allergens, and inclement weather.