I'm in the process of installing a Kerdi 48" x 48" shower tray that will be cut down to 35" x 35". My subfloor is level and is 5/8" OSB. My joists are on 16" centers. I've been looking through the Schluter Installation Guide and this forum, but can't seem to find any definitive information on subfloor requirements other than having to be level.

Will I be fine installing my tray over the 5/8" OSB, or should I be looking at putting down a layer of cement board (don't want to raise height too much)? The rest of my shower walls are Durock cement board.