I have a customer with cantilevered decks that stack one over one over one. The lowest deck has plywood decking and formerally had indoor/outdoor carpet. The deck above is standard 5/4 pressure treated pine. They had luck (for a while) with site bent aluminum installed between the joists to act as “pans”. Each pan was shaped to flow water away and out to a gutter(clever right?)Over time the 5/4 deck boards allowed dirt, organics and I assume pet urine to flow through and gather on top of the pans and in time the aluminum corroded and now the pans leak. Without removing the deck boards I am looking to waterproof the pans. One suggestion is to use a rubber based foundation spray by “RUB R WALL”. I don’t know if this will work but I need a solution. Please suggest