Mira Flight Shower Tray - Install

[wweesstt]

Hi, I am looking to install a Mira flight shower tray 760 by 760. I would have like to have removed the existing floorboards and installed battens and 18mm ply level with the joists. However, there is a stud wall running parallel to the joists sitting on top of the floorboards preventing me from doing this and I don't really want to take bedroom floor up or mess with the stud wall. If I screw down a 6mm section of ply on to my sturdy floor boards, cut a hole for the waste and sit the tray on top of this I assume it will work? I assume I will get an extended waste to work with this floor thickness?

Going for the Mira low profile since it has the option to be siliconed or cemented down and Roger Bisby seems to rave about these trays on youtube.

 

[Knappers]

What's wrong with tray on floorboards?
If for rigidity then 6mm won't do much, perhaps if bonded with gripfill but cement board would be better?
I wouldn't silicone a tray as not good if ever needs to come out.
Can cut relief in floor to fit trap if needed.