"Okay my crayfish sucked. Show me what you mean."
That made me laugh a bit. I didn't get a chance to try it yesterday, but I imagine your fibers were getting wrapped up, twisting, or coming apart. If you have squatch fingers as well it may make using them tough.
When you grasp the turkey tail feathers angle your fingers with the turkey fibers. Before you cut them put your finger about 1/4" away from the base. Cut them and keep them held tight, i suggested holding your fingers with with fibers to add more area that you can keep them together. Tie them in first with a loose wrap or two then add pressure. You have to be careful when you wrap the chenille and hackle that you keep the feather in mind. Bumping those things can split them.
You can use some marker and color the plastic as well. One thing that made me think about the turkey feather, was that others had had expressed that they thought the natural skin looked too shiny to resemble a crayfish, and thought that might be a better sub-in material. Going off of their suggestion you may want to dull up the plastic.
Looking forward to the crayfish picture.