A couple of places to look for cowl making tips;
RCU Composite Forum;
Fiberglass How to: Plug to Mold to Parts by DocJones199
How To Make Mold For Cowl by GSAV8R
Other places;
CST
http://www.cstsales.com/index.html Look in the Tutorials (top bar) for different tutorials in PDF format.
Steve Jones
www.fiberglassmoldmanual.com sells a comprehensive manual about making molds, parts, making plugs, multiple piece molds for complex parts and more. Lots of good info in the manuals.
Fibretech Great Britain
http://www.fibretechgb.co.uk/DefaultHome.htm has a tutorial for making a glass cowl from an ABS cowl under Working Tips.