Bill;
I've made some furled leaders using 4 lb. test Berkley "Vanish". While I have not used one yet a good friend and FAOL member says they sink like a rock.
I had read this post earlier and got to thinking about furled flourocarbon, came back and scrolled down so fast I missed Warren's post. He and I have been exchanging ideas on furled leaders for over 6 months.