That 'mission area' is of course of an AEW version, not a proper Shackleton at all. But you're right about the streams of water pouring in (whether on T/O or the cruise). Naturally when the modifications were done down at Bitteswell to put the AN/APS-20 and associated Gannnet rejects into the aircraft, only the RN specialists had any input, so nothing was done on/to the aircraft to improve 'crew comfort', including replacing the cockpit sealing and a number of other modifications that could have been done virtually for nothing as everything was being taken out and replaced.