Simply find some long vines, cut and allow to dry a day or two. Next, pull the vine around a small branch to break down and remove as much of the outer chaff as possible. At this point you will begin to notice the inner fibers separating. Peel long sections apart and start cording. It doesn't get much simpler than that.
Kudzu fibers are fairly strong if properly worked.
I have used them a lot for tying things and for the string on bow drill fire sets. The nice thing about elms is that the branches on the limps grow at 90 degree angles to each other. This makes it easy to get long strips of bark without having to worry about hitting a limb. Slippery Elm is similar to Hickory bark in its qualities. The wood is light and makes the best fireboard that can be found in my opinion.