iTunes Backup Fails

Hi there. I'm trying to backup my iTunes library using the Back Up to Disc... function. But for some reason in the middle of the 9th (of 20) discs, it won't burn any more. It didn't ask me to Insert Blank Disc like it would after the other discs ejected. So I tried to re-start the process by choosing Back Up to Disc... again, and this time checking the "Only back up items added or changed since last backup" option. It'll scan the library, say it needs 13 discs to complete it, and when I click Continue nothing happens. The iTunes status bar only shows an Apple logo -- no burning status or anything, and the drive isn't doing anything. I tried restarting the computer (and iTunes), I tried using different discs, but nothing seems to change. I don't really want to restart from scratch and re-burn 9 DVDs to see if the error replicates itself. Any ideas?

Also: I see most of the topics on iTunes Backup failing are greeted with "Use an external hard drive!" This will not work for me. I am backing up my library to transport it to the Mac mini in my car. External HDs need more power than the car can give it and Wi-Fi reception isn't great down there; also, I'm not too fond of the idea of leaving my car on all night to transfer 70GB of data wirelessly. DVDs have proven to be the sole reliable method for getting music on there. So please don't tell me to use an external HD! I would if I could!