Self-adhesive waterproof flashing tape 4" x 50'. Black. One roll seals 50 sq ft, on average.
Material estimator here: https://trexrainescape.com/materials-estimator/
What Is Trex RainEscape? A revolutionary under-deck drainage system.
-Uses a network of troughs and gutters to divert water from the deck -Shields the area below the deck from rain, snow, sun, and other elements -Provides 100% protection of the deck substructure from moisture
-Holds screws in place longer
-Finish the space with an under-deck ceiling and utilities such as gas and electric
-Brighten the area with Trex RainEscape Soffit Lights
-Easy to install
-Backed by a 25-year warranty