A nice plastic loop which goes around the main/traveler line works great when this loop is attached with a bungee cord that brings it to the center of the boat. My A-class has this ring in the center of the trampoline and the other side of the bungee cord holds the righting lines (under the boat) in place. I have almost no fight against the lines and rarely have it dragging long in the water.

Regarding length, Rick Bliss had a great system. Every time he sailed, he cut off one inch. By the time the lines got too short, they were worn out. Then add 4 inches and repeat (but only cut once per month). Eventually every line gets to an optimal point.