Ah, yes, I remember this. If I remember correctly, there is plastic on the bottom of the styrofoam insert and you turn the
hull upside down to drive it out the top. I was too cautious and to gentle at first, afraid I would break something. Needed a very large screwdriver and a hammer and had to really hit it hard, first on one end then working my way along it striking every inch or so to the other end to break it loose and then drive it out.