dont get the "salmon bungee" those are really long and sortof overkill for tarp tensioners (read: too much flex)
the Dipsy Diver Snubber is what you need, in 6 or 8 in. length. I use 6 in. at all 4 tie-outs on my MacCat micro. works like a charm. I have also used them to keep silnylon tarps taught while ground sleeping. Great thing about them is the snap swivel can be attached and removed very quickly.