Kevin, I've been reading this forum for quite sometime and thought I'd put in my 2 cents worth. In thinking about adding a line, Why not go through the front and rear beams in a complete circle. Add bungy within the beams just enough to keep things taught, but don't splice the bungy into the line, just use it as a "take up". This will allow you to make the line as long as needed. Keep the whole system from rotating by adding stop knots outside the beam endcaps. This would make a clean setup, however it would limit fore and aft movement to being within the scope of the length of the line and bungy... further thought, use the center trap bungy as an eye to keep the rope at the top edge of the hulls. I'm curious to know how this will end up.