Also, read some of the sticky threads here
, especially the one titled "Whoopie Sling Suspension".
An alternative to whoopie slings that accomplishes what you're trying to do is the UCR suspension. It's even lighter, but negligibly. Whoopies are more popular, but there are people in both camps. I've actually got a whoopie on one end of my hammock and a UCR on the other (don't ask).