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I was thinking of it as a single piece of sil with just hemming around the edges. If you wanted the cover and the shelf to be a single unit you could cut out a large semicircle to sew into a cone...

What I was thinking was a solid peice of Silnylon, Run shock cord in the lower edge to hold it tight under the suspension triangle. And use a mitten hook and a length of shock cord from the lower...

Or cover them with a Sil-nylon cover that goes over your ridgeline and hook under the edge of the pockets with shock cord.