Underdecking Trex RainEscape System Gutter system installed over joists and beneath decking, with troughs and downspouts that channel water to a gutter system. Dexerdry for Grooved Boards "gasket" for sealing gaps between deck boards, to create a water-shedding system with grooved decking. Inside Out Underdecking Metal paneling system that is installed beneath the deck framing. Woodgrain and solid colors. TimberTech DrySpace Panels Vinyl panel system mounted to the underside of the deck joists, white and bone colors available.