A portable cooling unit configured for use with a storage container, comprising: a desiccant unit including at least one exterior wall substantially defining an interior desiccant region, wherein the interior desiccant region is substantially sealed from gas transfer between the interior desiccant region and a region external to the portable cooling unit; an evaporative cooling unit including at least one exterior wall substantially defining an interior evaporative region, wherein the interior evaporative region is substantially sealed from gas transfer between the interior evaporative region and the region external to the portable cooling unit; a vapor conduit including a first end and a second end, the vapor conduit attached to the desiccant unit at the first end, the vapor conduit attached to the evaporative cooling unit at the second end, the vapor conduit forming an internal, gas-impermeable passageway between the interior desiccant region and the interior evaporative region; and a vapor control unit attached to the vapor conduit, wherein the vapor control unit comprises: at least one valve configured to control movement of gas through the internal passageway of the vapor conduit between the interior desiccant region of the desiccant unit and the interior evaporative region of the evaporative cooling unit; a controller operably connected to the at least one valve; a sensor attached to the controller; and an externally-breakable seal across the internal passageway of the vapor conduit, the seal configured to prevent the flow of gas through the internal passageway of the vapor conduit; characterised in that the externally-breakable seal comprises a gas impermeable membrane across the entire interior of the vapor conduit in a specific region. a desiccant unit including at least one exterior wall substantially defining an interior desiccant region, wherein the interior desiccant region is substantially sealed from gas transfer between the interior desiccant region and a region external to the portable cooling unit; an evaporative cooling unit including at least one exterior wall substantially defining an interior evaporative region, wherein the interior evaporative region is substantially sealed from gas transfer between the interior evaporative region and the region external to the portable cooling unit; a vapor conduit including a first end and a second end, the vapor conduit attached to the desiccant unit at the first end, the vapor conduit attached to the evaporative cooling unit at the second end, the vapor conduit forming an internal, gas-impermeable passageway between the interior desiccant region and the interior evaporative region; and a vapor control unit attached to the vapor conduit, wherein the vapor control unit comprises: at least one valve configured to control movement of gas through the internal passageway of the vapor conduit between the interior desiccant region of the desiccant unit and the interior evaporative region of the evaporative cooling unit; a controller operably connected to the at least one valve; a sensor attached to the controller; and an externally-breakable seal across the internal passageway of the vapor conduit, the seal configured to prevent the flow of gas through the internal passageway of the vapor conduit; characterised in that the externally-breakable seal comprises a gas impermeable membrane across the entire interior of the vapor conduit in a specific region. at least one valve configured to control movement of gas through the internal passageway of the vapor conduit between the interior desiccant region of the desiccant unit and the interior evaporative region of the evaporative cooling unit; a controller operably connected to the at least one valve; a sensor attached to the controller; and an externally-breakable seal across the internal passageway of the vapor conduit, the seal configured to prevent the flow of gas through the internal passageway of the vapor conduit; characterised in that the externally-breakable seal comprises a gas impermeable membrane across the entire interior of the vapor conduit in a specific region.