From your post it sounds like you won't be a GDMO until 2012, so I can only assume you are in foundation year 1. To offer some advice if I may, my understanding is that GDMO's on completion of training are posted by the Army to a medical centre where they gain experience in the primary care role under clinical supervision. I left the forces some time ago but to my knowledge there are no permanent post in Oman for a junior doctor. Complete your training first, walk before you try to run, you still have a long way to go and the Army will post you to where the need is greatest, MS binding principle I think they call it.
But if it is the sunshine you crave then I would ask for the post in Hawaii. Aye ask at AMD, Karabiner seems to know a fair bit on this stuff with the cadetships being curtailed to 10, he appears to be someone well placed to answer your questions.