Getting to work in Antarctica is not exactly a crap shoot. When I went to the South Pole as Communications Operator, the qualifications involved familiarity with a lot of equipment that one could have learned only with the US military. As I understand it, a lot of guys were interviewed for the job, and it was months before Holmes & Narver the contractor at that time tracked me down, since I had moved from the address on my resume.
It’s true that the application process begins early and some of the hires are last-minute decisions. Sometimes this happens because either the person the headhunters thought was best qualified was no longer available, had second thoughts, failed the physical or psych evals, etc. Anyway, applying now has you up front on the decision list, though it’s very possible you may not hear a word from RPC until August, or even September. There’s always time allotted for the necessary process of getting passports, physicals, and personal stuff in order. Also, there will be a pre-deployment conference of all involved personnel, including military, civilian, and NSF staffers.
BTW, I doubt that there is such a thing as “over-qualified” for a position on the ice. Any position will be a challenge for whoever accepts it and is deployed. In this vein, as well, you might consider applying for positions where you think you might be only marginally qualified. You may be more qualified (all things considered) ultimately than an applicant with twice you experience.
Be patient. Good luck. If you don’t make it this time, try again.