HI There, im about to layout Jackoboard panels and wetroom shower tray on my bathroom floor, whilst the floor is up im going to take up the uneven and gappy 100yr old floor boards and lay a new subfloor new. Question is, should i use standard flooring chip board, standard 18mm Ply or 18mm marine ply. Im thinking chip board should by fine as im using the tile backer backer board to tile to and water proof. If i was to tile direct to the board then it would be the marine ply. Im i correct in my approach? Many thanks