Cliff:
Overnight bags only provided to cabin staff though I have seen the occasional flight deck crew-member toting one along. Suspect they are available for purchase somewhere but they look very heavy (and very large).
Your overnight bags get checked and put in the baggage hold when reporting for duty so I can understand why they must be durable. Suspect they undergo the same torture test as the passenger luggage (find clip of famous Samsonite advertisement)
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Congratulations to Red Baron and hope to hear good news from the other applicants.