It would be an excellent idea if your friend could develop some serious stress regulation skills before shipping out, especially under (relatively) calm conditions. If these skills are solidly “installed” in advance, they can easily be called upon under duress and accessed pretty quickly, effectively and automatically. And once your friend can manage and commandeer those big swings of neurohormones that flood the body under super-stressful conditions, (sometimes setting up a loop that doesn't know how to stop itself from going back and forth from acute alarm biochemicals to dopey, sedating biochemicals, which is the essence of PTSD) there’s a decent chance that posttraumatic stress symptoms can be averted or at least significantly reduced.
So, yes, very good idea!
And the good news is, it wouldn’t take much for him or her to do this – maybe 2 or 3 weeks of practicing 'on manual', so to speak – once or twice a day, for roughly 20 minutes - in order to go on 'automatic', meaning that just after a potentially traumatizing situation, your friend could initiate that practice of relaxing and listening (on an MP3 or just in his or her head), and the body would follow suit and drop into that protective, self-calming state.
The Relaxation & Wellness imagery would be fine to work with, as would the Stress Hardiness Optimization program. Other good ones would be Healthful Sleep and Relieve Stress. I wouldn't start out with the very intense Healing Trauma, unless your friend has already been traumatized - that one comes in handy if needed for full blown PTS.
And if guided imagery doesn’t suit your friend, the same self-regulation can be delivered through the practice of mindfulness meditation, affirmations, yoga, qigong, biofeedback, simple progressive relaxation or breathing exercises - whatever suits. There are many ways to get to this same protective end point. And whatever works for your friend is the best approach.
Wishing for the best,