Track Shortener and Chugalug,
Speaking as an outsider, it seems to me that the trouble was that they were operating with seven-man crews. The essential minimum to "work the ship" was four: (Pilot, F/E, Nav and Signaller), that leaves three others. There are three gun turrets.
So if one of the remaining three men is a Bomb Aimer, either he has to spend 99.9% of his time freezing in a turret (for he can only function at his primary task when the bombing run is in progress), or accept the fact that the front turret is likely to be of little or no use in night ops, leave it unmanned, and generally make himself useful as the Nav's helper and general factotum.
Of course, if "Shräge Musik" had been anticipated, it might have been possible to squeeze in a ventral gun position as well as a H2S in the little space left after the long bomb bays - but he would have to spend all the time in that for it to have been in any use.
How we must have envied the Americans, who were able to provide two pilots for all their multis, a separate Bombardier (what did he do in his spare time ?) and gunners for all their guns ! (having said that, they certainly needed them !)
It begs the question: what use was our front turret at night (apart from helping to part-balance the equally heavy rear turret, which had a much bigger moment of force as it was further from the CoG).
Danny.