I just installed the shock cord tensioners on my SWT using HC4U's method. It was a breeze. I got the shock cord at Hancock fabrics ($0.74 / yd). I have to admit that looking at the directions above the clove hitch looks like it would let the shock cord slip through, especially when there isn't tension on the knot, but I was wrong. The clove hitch seems to hold really well so far.
This is a real newbie type question: I assume that you don't install tensioners on the ridge lines of the tarp. Is that correct?
Thanks for the tip and I appreciate the good instrucions and knot tying how-to!