Chris,

I just got back from a book store. There was a picture of using a clear trash bag and chopped up plant material to make a "bag only" solar still. It showed the bag having the plant material at the bottom of the bag. The bag was pointed down hill with a space for the water to pool toward the opening of the bag. The bag was shown sealed with a twist tie.

So the only questionable part was using barrel cactus. I was on an outdoor survival class, with PJ from Phoenix Parks, and he had Prickly Pear Cactus for us to chop up. We were making small solar stills with film canisters in the center. I got a little water in mine after about 2 hours. I did not taste it.