I think it worked.
I used:
singularity pull docker://quay.io/biocontainers/deeptools:3.5.1--py_0
which downloaded the Docker image and converted it to a '"sif" (singularity) image file.
Then I tried:
[aloraine@str-i1 nextflow_deepTools]$ singularity run deeptools_3.5.1--py_0.sif bamCoverage --version
INFO: Converting SIF file to temporary sandbox...
WARNING: Skipping mount /usr/local/singularity/var/singularity/mnt/session/etc/resolv.conf [files]: /etc/resolv.conf doesn't exist in container
bamCoverage 3.5.1
INFO: Cleaning up image...
which seems to have executed without an error - just a warning.