and embed some kind of a tension
member in them,

See..thats the whole problem..I just want something that doesnt require
any poles because I almost always camp where there are trees and the
poles add a lot of weight. Not so much of a problem in the boat but I
also like to use my equipment for hiking.
I think a simple square of fabric supported across the diagonal between
two trees and stretched across all four corners corners, two to the
trees and two to the ground, works almost as well and is much simpler to
fabricate. True, it does not take advantage of the arch effect of a
catenary parabaloid, but it doesn't need to. I find it hard to believe
that the only company that sells such a thing is Campmor and their price
is too high. A big square of rain fly material with a few loops or
grommets should do the job just fine...for less money.