In message , Charles Middleton
writes

Thinking about this a bit more I'm not going to be able put the shower on a
platform. I am presuming the platform is square. This wont be any good as
its the curved quadrant that's giving me clearance for something else -
namely my feet whilst I'm on the bog! Putting in a square platform is going
to remove that benefit.

Then make a curved platform......

I put in 900 mm quadrant tray a few years ago.

I cut a piece of 18mm WBP ply to match the size and shape of the tray
(actually a bit bigger on the wall sides as a bit went into the chopped
out plaster of the wall.)

Supported the ply on 4x2's so arranged as to allow the waste to exit,
and allow access from outside if necessary (though I used a top access
waste) Tray bedded down on mortar as per instructions. Waste runs under
the base to the wall then turns and runs along the wall to the outlet, -
it's hidden behind built in cupboards, normal boxing in would be fine.

Fiddliest bit is cladding the curved open base.

In the end I cut pieces of scrap 2x1 to stand vertically under the ply
flush with the front - spread along the curved front. - they fit tight,
but I also glued them in place. Then I used a couple of pieces of white
UPVC trim strip screwed to the timber (screws covered with white caps)

IIRC, I used two pieces of strip (one cut down) one above the other
(total height is about 120mm I guess) as strip of the suitable size for
one piece was not flexible enough.

I'm pleased with the final result.
--
Chris French, Leeds