Thanks Ranger for pointing out those Figure 9 rope tightners, they look like a quick and easy solution to running a tarp line.  I'm into my knots but fast and easy is the goal and these look like they might actually be an improvement on a trucker's hitch.  Has that been your experience?  I went into their site and noticed a product they call "Cam Jam" which I might try as a way to tie down my tarp.  Sometimes these clever little gadgets turn out to be more of a pain in the ash than a help but then sometimes they really do what they say they will.