I happen to live only a few miles from the Dimension Polyant facility. My wife swung thru there for me last year, and asked about purchasing some VX-21 for me. No one seemed to know what that was,(even though I sent along all the specs I could find on that particular product) informing her that they manufacture many configurations of their product to whatever specifications their customers require. They do have both a sailing AND an outdoor fabric division, and seemed very willing to talk with my wife about what I was looking for, interupting their Christmas party to send her off with 2 end rolls for me totalling around twelve yds at a VERY cheap price. It's nice stuff, two different fabrics, but both have the waterproof top layer, the grid, and then a polyester scrim inside. At any rate, it might be worth calling them directly to inquire about an end run of something suitable for your project, they seem very well informed about possibilties for their product.
One of these days I 'll try to get over there myself...