A cover for covering an array of sample tubes during an incubation process. The cover has an upper panel and protrusions extending downward from the upper panel. Each protrusion has an upper seal and a lower seal. The upper seal includes a first conical section that tapers from a first diameter that is larger than the inside diameter of a corresponding sample tube to a second diameter that is smaller than the inside diameter of the corresponding sample tube. The lower seal includes a cylindrical section extending downward from the bottom of the first conical section. The cylindrical section has a diameter selected to create a capillary seal, in the presence of a liquid, between the cylindrical section and an adjacent portion of an inner wall of the corresponding sample tube.
