Unless I misunderstood the backup question, a backup of any internal partition[s] should be placed onto any available, affordable, trusted, external media -- be it usb sticks, DVDs, platter-driven HDs, SSDs, or even attached NAS devices.
Because the main reason for creating a usb or dvd boot is to make restorable backups, I recommend that the boot will lead to a backup onto any other external media. Putting a backup onto a usb boot is not a good idea; naturally a dvd boot will be finalized, so any other write action is impossible.
I've used Acronis True Image, Image for Windows, and Macrium Reflect usb and dvd boots. I've never been successful in making a WinPE/xyzPE boot with added stuff -- so I will listen in and learn alongside you!
Edited by RolandJS, 17 November 2016 - 06:09 AM.