......a more isotropic layup for the top deck .........
I'm pretty sure "isotropic" is the one property NOT available for any fiber reinforced plastic.
regardless of the method to determine the necessary strength and stiffness (trial & error, copy, calculation, guess) the layup properties in any particular direction will always be dominated by the fibers aligned in that direction (no fibers = no strength)
..maybe thats what you were suggesting?
regarding Johnney's layup:
if you do any math , i'm sure you'll find that
1/2 " core with 18oz of glass (top and bottom) in high stress areas is a good place to start.
divinycell core is ok but some have found it to be a bit brittle and fail over time,
corecell ( or similar non-cross linked pvc foam) has a reputation for being tougher and more durable with its higher 'allowable strain'.
Its not often that you'll find a legit use for carbon if the bulk of the board uses glass.
generally too stiff, too expensive and the light weight is overshadowed by all the other ingrediants.
Using the top and bottom cloth to overlap the rails will give good reinforcement.
Its probably a bit more difficult that 3" tape, but less sanding and fairing to get a clean finish.
i would have no problem using aeberl's recommended layup.
Just remember the flexural strength of his balsa core will be a significant contributer to the overall strength of the board. Something you will not get from any of the pvc foam cores.
folks on yahoo board building group are an excellent resource for what already works if you dont wish to experiment.http://groups.yahoo.com/group/boardbuilding/
search there for common layups.