Ubuntu LTS, Backblaze and Duplicity isn't a good fit.
This docker container wraps duply, and contains newer version of Duplicity that works with Backblaze.
latest
(Dockerfile)
Use the docker container the same way you would use duply.
Example:
docker run -u $UID -t -v $HOME:/data --rm aheimsbakk/duply-b2 usage
Remember to enable GPG option in duply configuration.
GPG_OPTS='--pinentry-mode loopback'