Don,

I made one out of the lightest weight coated ripstop nylon I could find (Seattle Fabrics) for some of my off-trail backpacking trips. There is not only an arc to the edges, the seams that join panels overlap in an arc as well. The external dimensions should be symetrical (square, diamond, or kite shaped). I figured out the arcs by trial and error. I pinned the panels together to see how it worked before sewing them together. The drawback to making my own is that there does not seem to a fabric available that is as light as what the tent makers offer in their product. I could get what I want from sailmakers, but there would be not cost savings. Also, lightweight coated spinnaker cloth tends to be very noisy. What I have made works well for kayak camping though, since it does not end up carried on my back.

Ted

: Has anybody made one? Is it just an arc on the edges, or is there some
: special shape about it? Seems expensive to me, a couple hundred bucks for
: a chunk of ripstop nylon.