The parting board that we used at the time was a PVC 1/4" plastic that was heated for the curved section of the wing.

Now days you can use anything that is non porous and will not soak up the wax/pva barrier. I have a freind that uses styrene sheet that is shored up to the plug.

Takes time but yields a almost seamless joint.

See vicrc.com for some good pics of molds. He is a local guy that knows what he's doing.

Steve