Don't put all your eggs in one basket, so of course apply anywhere you can to ensure work for the summer. That being said bases, especially in the spring, are always fluctuating. Sometimes people don't show up, sometimes people get jobs in bases they prefer to be at and quit the base they started at, some show up and don't like the job right off the starting line.
I know my base is doing interviews for positions still, 2-3 open, and at least 1 more opening come the end of May. Whether or not the hirees have been decided yet I can't say as I'm not part of that, but I know they are still deciding. Shoot out tons of resumes and hope for the best. Remember, highlight the important stuff on a resume for the type of work you are applying for. Camping, travelling, labour experience, jobs that require safety standards and gruelling hours, small engine work, GPS useage, and teamwork are all keys to a crew member position.