The hull thickness is a given at 1 foot.
However, the hull inside (substrate) is attached to a secondary frame, which is then attached to the primary frame via 2" flexible rods. Then, the outer hull layers are attached to the primary frame.
That means, you have the hull thickness, the thickness of the secondary frame (undefined), the length of the connecting rods, and at least *some* of the depth of the primary frame in the total thickness. You might be able to nest the secondary frame entirely within the major members of the primary frame, but doing some rough guesstimates on member thickness, I can't see how you'd get away with less than 4 feet, though maybe there's a way to get it to 3...
Point being,the cross-section areas spec'd for the primary frame's members are huge. On the order of parking deck reinforced concrete beams. Your looking at beams 3-5 feet deep to accommodate those areas, IMO.(see pages 18 & 19 of the manual for space frame specs).
The Primary Truss Frames are an average of 1.27 m^2 in cross section. If they were a square, this would mean that each side was a little over a meter, let's say around 3 1/2 feet. They could be rectangles, either narrower and deeper or wider and shallower. These are spaced an average of every 25 m across the hull. The exterior hull would be affixed to these, like how the plywood sheeting is nailed to the 2x4 studs of a stick framed house. The difference is that on the house, the studs are internal to the wall and a layer of drywall covers them on the interior for a smooth finished wall, but on the starship, the inside of the exterior hull is the interior wall and the frame members (the studs) simply protrude into the interior volume. As much of the interior volume of the ship is discreet sections designed to be swapped out, I posit that these sections are designed in such a way as to fit between the primary members or incorporate them into the interior design in a way that makes them inconspicuous.
Anyway, I'm not just randomly nitpicking stuff, here. I was playing around with Blender, and took on Enterprise D as a fun little architectural project... Thought maybe I could build it with the bones...
Good luck with your Blender project! that's quite the undertaking, I hope you post your progress, as I'd love to see it!