Corrugated cardboard, die-cut and numbered, forms the frame of a
fibreglass dinghy mold. To it you fasten a wooden breast hook, transom,
seat, gussets, and gunwales. Pull the cotton-jersey "sock" over this and
harden it with resin. Two layers of fibreglass and resin go on, then a
wood keel and rub rails. The cardboard is pulled out. Kit for 61/2 foot
dink is $89.

I found this ad with three photos in a 1960 Popular Science magazine. I
found this interesting. Thanks, Ted in Mich