what Jedi said pretty much summed it up the OP’s question.
but to my knowledge i don’t think setting the ‘booktype’ is required as far as XBox360 stuff although it is recommended. probably because it might be easier for Microsoft (when on XBox Live) to detect your backup if it’s not a original by attempting to tell if the disc is a DVD-ROM or a DVD recordable. and if the booktype is setup to DVD-ROM they wont be able to tell for sure since DVD-ROM drives cant tell if it’s a DVD Recordable or a genuine DVD-ROM… but to my knowledge Microsoft has not banned anyone because of the booktype stuff. so take this for whatever it’s worth
but to sum it up… get some Verbatim DVD+R DL media and then you can set the booktype to DVD-ROM and all will be good