Doug,
my memory being what it is I cannot recall the Nav coming aft to brief the team leader. When I was on JATE we had a special harness made up for the ALMs in order to carry two MK4 portable oxy bottles. A mite cumbersome but it did the job. As regards running out of puff when the a/c climbed I once had the same sensation on a route trip. Did the scan check and got back to the flight deck feeling less than A1. Looked at the cabin alt and it was passing 15000 ft. Smacked the eng on the hand and pointed. Instant switch flicking followed and normal service was resumed.
On the tanker I always stayed on oxygen until the safety valve had been persuaded to close post tanking.