air tight?

when you guys place the sub and terminal? into FG boxes how do you make sure its air tight?

Usually mold in a piece of mdf under the fiberglass to give it a place to fit and cut out later. Or do what I do and drill a hole and run the wire through and add silicone to make it air tight. If you already have the hole cut, sand it smooth run a bead of bathroom silicone calking under the terminal and let it dry and install your terminal. Also automotive gasket material works well. Something along thoes lines.