the luxury of being able to book months in advance. It really would be a huge step forward if a proportion of the rooms were set aside for current serving personnel who don't necessarily know whether or not they will in the country next week, let alone be able to arrange their diaries months in advance.
Holding back a few rooms might be a good idea.
Once I was delayed in UK before RTU and shared a twin room with a Gp Capt also caught short. Another time I was able to use the club next door. I was in town and caught when 7/7 shut London; Mrs PN was able to book me a room.
As for arranging your diary; I learnt years ago to book early and cancel late. Unfair maybe but that was the system. Now the book early can be months early; anyone booked for the Olympics yet?