I offered to install a shower tray for someone. The tray sits directly on the floor joists, and the rim will be level with the floor surface assuming it's tiles on 18mm ply (and as belt and braces, I specified marine ply for the area around the shower).
How should I seal between the shower tray and floor butting up against it, bearing in mind that some water will routinely be walked out of the shower onto the floor in front of it (and it's a very shallow show tray anyway)? As it happens, the floor joists already slope slightly towards the shower tray, which may enable any spilled water to run back into the shower tray, as long as the seal between it and the floor is good.
I believe the tray is enameled steel, but I haven't actually seen it yet. Under the tray, I may recess 18mm ply between the joists with top surface level with the joist tops if the shower tray would benefit from this, and that could extend a little way under the main 18mm ply floor in front of the shower.