With such a heavy hull, the ballast ratio needed to be quite low to avoid an idiotically high DLR, so they are quite tender. I sailed on one years ago she was called 'Rolling Stone'.
Friend built a 34ft Pinky gaff ketch from Jay Benford's board. He has professionals plaster it and it was smooth enough to pass as GRP. Hull thckness was around 20mm. No problems with the hull for over 30 yrs until he got biffed by a big ship in the Atlantic and had to abandon. He did remark that he would not use the method again. Benford stopped promoting it a while back. Not because he thought it was wrong, but because of the general bad reputation of the method.
I recall someone posted a link on here to a video about an American couple who sailed around the world on their old boat, got wrecked on a reef, salvaged what they could and then recreated their boat in ferro on the beach (amongst other adventures). I wish I could remember what it was called.