Disabling iMessage while travelling

Simple answer, yes.
If you want SMS to arrive at your phone there must be no other device left active that can possibly pick up the iMessage.

Otherwise Apple considers that if any device received the iMessage, it is considered delivered & will not try again as SMS.

Related question - How to tell Messages "I'm not at home"? which remains unanswered, despite the great efforts of one member; but shows promise for Yosemite, if not Mavericks.

When there is not any internet connection SMS messages should be delivered to your phones, so you should not need to disable iMessage anywhere. However just to be on the safe side, I would recommend you to disable it. It would be a fail proof way to feel safe about SMS/iMessage mystery.

If you use only your phone number as your iMessage account you can just disable it in all your devices to be sure that you will get all SMS messages.

If you have any e-mail address associated with your iMessage account, you can just remove your phone number from iMessage accounts in your devices and keep your e-mails. That way you can still receive iMessage, whenever internet connection is available.