The typical "honeycomb-sandwich" construction used by most FSAE teams for their "tubs" is, for the most part, completely UNNECESSARY. This applies to both the AL-AL and CF-AL (or CF-Nomex) honeycomb versions of such tubs. By the very meaning of the word, a "monocoque" (= "one shell") structure carries the majority of its imposed loads via stresses that lie IN THE PLANE of the shell. Such shell-like structures need very little bending-stiffness of the shell-material itself.
{snip}
Anyway, local reinforcement of point loads applied normal to the shell (eg. wishbone mounts) can be done with CF-"top hat" sections, either incorporated in the middle of the ~8 plies, or glued inside or outside the shell. The sides of the cockpit (ie. the "SIS") can be similarly reinforced. I would do a cockpit-upper-side "P"-section that is designed (and tested!) to carry all side-impact load. As such, this strengthening of the cockpit-rim would greatly improve overall torsional stiffness and strength.
As I have suggested many times before, similar "true monocoques" can be done in Aluminium (using 1 to 3 mm thick Al-sheet, as used on many small boats), Steel (I would use mostly the super-cheap 0.6 mm thick "zincalume" used for roof-flashing here in Oz), or Plywood (2 to 10 mm thick marine or aircraft-ply). All these would be much quicker and cheaper to do than anything with a honeycomb-core, and have at least as good performance.
To repeat, the shell-material of a true monocoque DOES NOT NEED A SQUASHY CORE! Using such is blindly following the flock. It surely ain't engineering!
~o0o~
Z