Back to the subject.
This link is to an interesting PDF file on how to make
centerboards. http://www.single-handedskiffs.com/images/centerboard_construction_final.pdf
The direction now in A-class seems to be moving to CBs with a cord length of about 150mm and a thickness of 10-14%, I don't know of the foam can be cut to those dimensions over the span of 1.25 meters, but it might be worth a try.
I think I would Vacuum bag it (let the bag hang down outside
the mold and use the thinest bleeder/breather I could find)
then clamp the hole thin together.