Audiobook Builder keeps it simple.

I just wanted to load my audiobooks on my iPod so I didn’t have to keep switching disks while driving or working. This app made it simple and lets me “read” a lot more than I would if I had to wait for quiet moments to crack an ebook, novel, or paperback. Its been my go to app for a very long time. I agree with the suggestion that it would even be better if there was only one file instead of part I & part II.

Chucklet about Audiobook Builder, v1.5.5