I made my torsion box body up out of a series of smaller torsion boxes. Seat, rails, body sides, scuttle, seat back; etc… all out of 6mm ply. Built them as as true and straight as I could, Then bonded and bolted them all together. It is, as far as I can tell so far, immensely strong. I also filled all the void spaces within the lattice with expanding foam, which is definitely optional. All the metal spinny bits bolt on via subframes made from aluminium plate or extrusion.
It’s definitely a unibody rather than a monocoque. It’s an immensely pleasing object to have hiding in the garage.