I use latex tubing found at the hardware store. 1/4" internal diameter stuff takes some doing to stretch over the endcap, but is cheap and since it comes in 10-foot tubes but only used an inch at a time, doesn't feel bad to replace as it gets chewed up.
a little hello from France, near toulouse, near the pyrenees, the mediterranean sea and the ocean. I am 58 years old, a good experience in 2 lines precision kite and I await the delivery of my first Revolution Reflex RX. Other passions, photography and large radio controlled gliders, between 6 and 8 m wingspan. Have a good day.