I'm with RDH - I think Tyvek would make a good shelter, but as a still, not so much. I am curious, though, if anyone has tried this as a still:

Line the still bottom with a black plastic bag, put your materials on that, setup your drip container and then put a clear plastic bag on top. That seems like the best possible scenario and in theory, you could just pee on the black bag or put salt water directly on it and it would keep all that moisture from falling back into the sand or ground.