> Structural members being bent develop tension stresses in one face and
> compression in the other face (tension in the face becoming mone convex);
> the material in between developes shear stresses (sliding forces between
> the faces). The styrofoam would not be capable of developing the shear
> stresses. The result would be two epoxy/glass layers in stead of one
> structural sandwich with a major reduction in strength..

If styrofoam is unsuitable, what kind of foam strips will be nice for such work?

The following products are not suggestions, i have no knowlege, but these names come to mind: Nomex, Divinycell, Airex.

Ray Jardin did use 3/8" Airex as core material, description o his method to be found at

http://www.transport.com/~ray316/kayak_construction/kayak_construction.html

But he did put the Airex on a male plug, so I guess this kind of Airex would be much too soft for strips on a strip-built.

Jan Gunnar