Merge .pdf files in .mobi with kcc and pdftoppm
Install the requirements (I assume that you alredy have the apps Kindle Comic Convert and the pdftoppm instaled on your linux-machine). Move the merge-pdf-to-mobi to your $PATH.
python merge-pdf-to-mobi --pdf PDF_FILES
--cover LOCATION_TO_THE_COVER
--output OUTPUT_FILE_NAME
--server (y/n)