I have used sil-nylon tarps on occasion out here in the desert in combination with a bug bivy and they work pretty well. Although I now tend to use a 1 man Sierra Designs tent as it does not really weight much more than the tarp bug bivy combo. I would love to live in terrain where a tarp was all that was needed, but I have not found the Sonoran desert to be one of those. The tarp I have is from http://www.owareusa.com/.