skiffer wrote:
.... snipped
Is there an alternative to silicon? I have in mind a qaudrant sealing
strip which could be abrasively cleaned and would shed water? Maybe
bedded onto silicon?
Thanks

I did exactly that. I filled the gap between the tray and the wall with
silicone, then cut some ceramic look-alike plastic quadrant extrusion to
be an accurate fit around the tray/wall joint, then put a VERY large
bead of silicone on the joint and pressed the extrusion into the bead
until it made contact with the wall and tray, then removed the large
amount of excess 'cone.
It's been several years now and looks almost "as new". I think the
quadrant came from Tiles'r'us.