As well as for take-off/landing, bone domes were required down the back of Victor tankers during refuelling. I never had an "all in one" helmet, and was quite happy with my 2-part Mk 1a, as several hours in a cloth helmet were a lot more comfortable than in a Mk 2 or 3.
tartare - have a look at the
V-Force Reunion website - you should find a lot to interest you there and some very good pictures on the gallery.