Your spending way to much time on this..
This might help
http://www.cstsales.com/tutorials/fiberglass_mold.pdf and
http://www.cstsales.com/tutorials/fiberglass_parts.pdf
PVA is just an extra safety net, if you use a good mold release wax it will work also..
How about some photos of the old cowl (plug) so I can see what your doing.