Casting a hull over a carved plug is a good solution for many kinds of boats. It certainly would have worked on the last ones I had occasion to make, which were eighteenth-century carvel-built hulls.
The Grand Banks dory, though, is an exception. I guess it could be done, but I think there are easier and better ways.
The typical dory has four or five lap-straked planks on each side. The typical schooner carried ten, stacked up in two stacks on either side of the waist. (I don't think I've ever seen a picture of a dory with a cover on it.)
I figure in 1/96 scale it ought to be practical to make them about the way the originals were - out of individual planks, upside-down, over a wood mold. Then the boat gets flipped over and all the internal parts get added - frames, thwarts, etc. (A lot of that detail won't be necessary for any of the boats except the ones on top of the stacks.)
I've got some holly veneer that might work. I'm thinking, though, that the right material may be Bristol board (a fairly heavy, hard-surfaced white paper that's remarkably easy to work with). I've got several good sets of plans (including those by Chapelle and Willits Ansel, and an odd little book called The Dory Model Book, by Harold "Dynamite" Payson).
But the vac-forming idea has its attractions. It would be a lot quicker, it would guarantee consistency from boat to boat (important so they stack properly), and I could add the internal details as necessary from wood or styrene. I'll have to meditate more before I conclude whether that machine would be a good investment - though I could certainly find more uses for it.
Bluejacket sells cast metal dories, but - with all respect to Bluejacket, one of my favorite manufacturers - they really aren't very good. The planks are way too thick, the "plank" detail is crude, and they have flat bottoms. (That's an absolute no-no for a Banks dory. The bottom is supposed to be flat in cross section, but it sweeps up at the bow and stern.) The cast metal ones that came with the Model Shipways Elsie are pretty poor as well. About the only 1/96 dories I know about that might work are the styrene ones that came with the old Pyro/Lifelike/Lindberg Gertrude L. Thebaud (aka "American Cup Racer"). Each kit has only four, and given the prices those kits are claiming these days ( http://www.oldmodelkits.com/index.php?detail=26081&cat=Civil%20Ship&manu=Lindberg&erl=Lindberg-1-96-American-Cup-Racer-710 ), the thought of buying three to get ten dories is pretty much out of the question. Further medititation is called for.
The schooner model itself is coming along pretty well, now that I've reconciled myself to the fact that I'm just not as good at such things as I was thirty years ago (and that I need magnification for much of the work). I've been taking in-progress photos of it; once I become genuinely confident that it's actually going to get finished, I intend to start a Forum thread about it.