Gato, I assume that you are talking about my beam construction. Okay,here is my comment:

The use of different fibres for a layup-skin has proven for me its strength in my windsurfboards. I use that mixture already for years with content. The foam by the way in the inner part of a surfboard contains a lot of air which can even flow (alive), because the foam is not completely closed-cell. So the internal humidity with regard to water condensation-point is also fluctuated. Besides that, I open the boardhulls after sailing because of depressurizing for heating by the sun.

My beams now ,in contradition with above, are completely sealed off the external world, they are airthight and ofcourse waterthight. The PU-foam is closed-cell; so in my opinion the humidity status of the wood is frozen and I don't see the problem.