Have a look here: http://duplicity.nongnu.org/
docker run --rm
-v $PWD/.cache:/root/.cache/duplicity \
-v $PWD/.gnupg:/root/.gnupg \
-v /:/data:ro \
agileek/duplicity:0.7.18.2 \
--full-if-older-than=6M --allow-source-mismatch /data gs://my-bucket-name/some_dir