A seal structure includes a container, a sealant applied in liquid form that cures to a gel, and a cap that applies pressure to the gel. The container surrounds at least one opening in an assembly for the passage of elongated members such as wires. The container defines a chamber that is in communication with the opening and surrounds the wires passing through the opening. A closure spans the opening and is in contact with an inner end of the container. The chamber and the at least opening are partially filled with a predetermined quantity of sealant in liquid form, which cures into a viscous gel. The cap is configured to engage with the container and includes a platform that is positioned within the container and in contact with the gel sealant. In this arrangement, the cap applies positive pressure to the gel sealant.