hello,
Like it says in the first article that was linked to, there are 2 types of styro. the blue one he recomends is extruded and doesn't soak water. the thing he apparently doesn't know is that the bond between the glass or carbon and the extruded foam is shortlived unless specific steps are taken. the reason i know this is the winsurfboard business on Maui has been there. Thousands of boards were built with the stuff and they mostly all delamed eventually. Apparently if you vacumebag sheet foam to the extruded styro the lam will hold however. there may be other solutions which are prolly secret. The winsurfboard builders ended up staying wth the beadtype styro even though it soaks water. We encase it with sheet foam which is vacumebagged, so they only leak after a pretty good hit. these boards are custom and some are just sailable plugs for the molded versions that are made in Tailand.
you can just glass the beadtype styro by hand and as long as you get it out of the water as soon as you get a hole it will last quite a while as long as the skin is plenty strong. glassing w/ carbon lasts the longest and comes out the strongest for the weight.
styro comes in many densities. we use mostly 1.5 lb. 2 lb will be more unbreakable but heavier because if you cut back on the skin weight the board will break since styro isn't very strong. the beauty of the beaded 1.5 lb styro is that it is very easy to shape. Both with a hot wire and with the planner/sandpaper process. Shaping extuded styro is almost as tough as shaping wood.
As far as hollow molded daggerboards go, i would imagine that they are done in an autoclave w/ prepreg and the process would be a carefully guarded secret, or at least you would have to go to school to learn about that process.