I'm afraid those enclosures are for a pure radius curve type tray i.e. a tray which is 1/4 of a circle. Open the PDF in my OP and you'll see mine has straight sections at each side of the doors and a smaller radius inbetween - so the radius curve type won't follow the tray.
Apologies if this is in the wrong section, it didn't seem to fit obviously anywhere else.
I have a shower cubicle which sits on an 850 x 850 quadrant tray with straight sides - see PDF here:
http://www.railwaysarchive.co.uk/temp/shower%20tray.pdf
The existing enclosure is leaking due to...