If you have three, you want one in front of the elevator hinge line, and one behind the hinge, it helps keep the elevator and stab from flexing. Glue them into the coro with a bit of Polyurathane glue, and put something heavy on them on a flat surface so the stab comes out striaght and flat.

The third one you can just slip inside the vertical stab to keep it from flexing too much.

Also, another floyd tip, make the vertical stab bigger than what you think you might want. It will help with the stability and help you turn tighter. (a bigger vertical stab keeps the plane going straight at high AOA, which does make the stall occur a little later).