How about this:

http://www.rei.com/product/684087

Put it under a tarp if rains is a possibility:

http://www.rei.com/product/627834
http://www.rei.com/product/655940

I have not used any of these products personally, but that's where I'd start looking. Lots of different tarp options available. I would want netting for bugs to add to that though.