bpLite

Another source of surgical tubing is wrist rocket (the slingshot) replacement tubing. I know Walmart carries them. You could probably make 4 tensioners from one package.

I think this link shows the shape and tie-outs fairly well. There are 12 tie-outs along the side and the rest on the "top" of the tarp, kinda like pull-outs. http://www.sportsmansguide.com/zoom/zoompop.asp?i=79977i2%5Fts%2Ejpg&h=320&w=320&bgc=FFFFFF&ui=3&mz=2&cf=2&a...

I bought this one recently and it's light enough. It's kinda a cat-cut shape without an ties on any middle edge. The corners have both a grommet and tie.