Hi !!
What I do when I add audiobooks with multiple audio files is create an .m3u playlist.
I directly add this playlist with the name of the audiobook name to caliber and then (manually) copy the files to the caliber folder.
If you click on the audiobook, it will open the playlist with your player and it will have all the files of each chapter loaded.
The .m3u file is something like this:
(you can edit the .m3u file with any text editor)
Code:
#EXTM3U
my_audiobook_name_01.mp3
my_audiobook_name_02.mp3
...