The aft portion of the flag level bulkhead structure is not square - there's a little extra on the starboard side with a flat bulkhead between this portion that extends aft and the port side which ends earlier. When I've seen design like this there is often an entryway there, be i t open archway or watertight door. None is depicted on the kit as this surface is actually the joint between the two halves. Plopping a spare photo-etch door there might save me a touch of work.
None of the online walk-arounds or galleries I have found shows this area clearly and the one basic plan I was able to find showed the aft side of this structure as squared off, so I'm a little bit mystified. Photo 115 on this gallery Lars posted appears to show a watertight door on the aft bulkhead, potentially a porthole inboard of that, with a shelf below. It's about a third of the way down the page.
Anyone know for sure?