Submitted for your approval (or disapproval, as may be the case :-P)
I am in the habit of frequenting the $1 and $2 bins at WM, and when I find something that may be waterproof I will get them to cut me a small sample strip. I then take the sample strip to the bathroom and check it out under the faucet (I know, I know...weird...). Anyway, I recently found this absolutely waterproof fabric for $1/yd and turned it into a HH Monsoon clone. I made it a bit longer to accommodate my Explorer. I recently hung under it several days last week and made it through a nice storm completely dry. I used flat-felled seams, and altered the design by putting a seam on each edge rather than in the middle of the tarp.
The man in the ENO is NOT me! ;-)
The last picture is of the hammocks for me, my two sons, and my nephew. We hung out several days testing gear for an upcoming hike.