Were you thinking of having a fire-resistant patch to allow the stove to be used inside the tent inner and protect the tub floor, because to be honest there isn't much room in these sizes of inner for that sort of thing along with yourself, sleeping gear, and the like? On the other hand I'm quite keen on the idea of sizing the vestibule to make it far more convenient to bring the cooking under cover, which is one of the reasons it has been made so large. In the standard configuration you'd have the stove on the bare ground. In fly-only mode the footprint may be sized to cover the entire area including the front half (normally vestibule), TBD on this, though I'm sure if it was, it could also be unhooked and folded back under itself to be a half-footprint just for the rear sleeping area, again allowing cooking on the bare ground (for when the meal boils over right?). Either way I'm sure you'd be fine. Fly partly open for ventilation? Even if not, the fly doesn't go down to the ground. This was to better control condensation but I guess the same applies for carbon monoxide. An important point to have raised that I hadn't considered.
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