Ok, I have made this work: I created a Singularity container from the Docker image
linuxserver/calibre.
On the CentOS 7 host I've installed Singualrity simply via `yum` and this loads the container smoothly. Calibre then can even run as GUI application using the X11 forwarding from the host! :-)
One problem tough are external applications calibre calls (e.g. a PDF viewer for PDFs). These would need to exist in the container, but I haven't gotten that far yet.