Tray having a container receiving space and a stepped outer sidewall including a lower step and an upper step, a cooling unit providing cooled air to the space and having a housing with a stepped base that includes a lower step and an upper step, the cooling unit venting exhaust from an end distal to the base, a plurality of containers each having a perimeter flange and, when the container is inserted into the space, portions of the flange are seated on the respective lower steps of the tray and the stepped base of the housing, and a cover configured to sealingly contact the upper steps when the cover is in a closed position, the cover shielding the containers from the exhaust, and being movably attached to the housing and movable along the housing in a range that includes the closed position at which the cover contacts the upper steps.