I saw this in Wally World:
http://www.walmart.com/ip/First-Up-T...-Wall/19902104

It is 10' x 10', lightweight and $14.

I'm going to try it out as a hammock rain fly.

It says on the package tag, "This material is not waterproof. It is extremely water-resistant. Touching the fabric when wet will cause water to wick through the fabric."

I'll give it a hosing down, in the backyard, this weekend and report back.