spongy bathroom floor

[reilym]

I thought I remember reading about this topic, but I can't find it. The floor in my PW Lexor's bathroom is molded plastic and it's fairly rigid, except for one spot between the toilet and floor drain. It gives me the heebie jeebies every time I step there and feel the floor flex. Anyone else have this problem and have a solution? It would help if I knew how these floors were installed, but it looks like it would be difficult to remove it to add additional support.

I was contemplating using a rigid expanding foam injected into a hole drilled into the 2" vertical threshold below the surface of the floor, with extra holes to allow the foam to escape (see attachment). It would be relatively easy to fill the holes after the foam cures. Thoughts?