Here in our kitchen we have a couple of plastic cutting boards that are about 5/16 inch thick, sort of a milky white translucent plastic (found in many discount stores). They actually float, although mighty low in the water and I'm not sure all are of similar density, it might take experimentation. They may come in large enough sizes for your need (they can be cut to size/shape -- I used one as raw material for a project). The advantage would be they are solid material and easily rinsed off. I suppose one could drill a small hole in a corner to hook and lift them out.