If you don’t have the bottom, you don’t have a torsion box. The strength and stability of the torsion box comes from the shearing strength of the two sets of glue joints separated by the height of the box.
If you don’t have the bottom, you don’t have a torsion box. The strength and stability of the torsion box comes from the shearing strength of the two sets of glue joints separated by the height of the box.