I've seen quite a few different ways of making guy lines self tensioning for use in poor weather, or for keeping silnylon tarps pitched tight during rain ect.
I've been using this set up for two years and its fool proof. No silicone tubing, knots or anything complicated. It can be added in seconds and weighs next to nothing.
You simply take heavy duty rubber bands (mine are pink, but free!) and using 2-4 (3-4 being really lousy weather) loop them through the eye of your tarp, fold in half and clip on a mini krab. If you are a gram counter, they can simply be used with a toggle, or even larks footed through the eye, and then larks foot on your guy in turn.
Its always worth using two (in case one fails) but I've never had a problem, even in severe weather.
I hope this was of some use and a simple alternative