p5 tongue and groove

Have tiled my downstairs WC using 600x300 porcelain tiles. I have some pipe work at low level that I need to box in then tile to match. The boxing will be about1800mm long 200mm high and 70mm from the face of the wall. Is it ok to use p5 for the boxing with 2x2 inside to support the 90º...

Hi, Mrs and child have been sent away till end of the month so that I can redo bathroom. t&g chipboard got significant water damage. is it ok to go with P5 t&g chipboard replacement or there's a better alternative? Wall and floor will have cement board before tiling. Thanks Sam