Like said above, usually there is a gasket on the sub, or at the very least the enclosure has carpeting that will act as a decent sealer. But yes, if your sub just has a bare metal frame to go against the baffle, and your box is not carpeted (or not carpeted where the sub mounts), then you would want to use some sort of sealing material. What material to use, and how to go about it, is a fairly common sense application, so i wont bore you guys with describing that procedure.