There's a pretty good image out there already for Duplicati, which I installed the other night. https://hub.docker.com/r/linuxserver/duplicati/ I've played with it a bit, but haven't fully figured out the backup strategy, where to put things offsite.
As a (former) CrashPlan Home Customer, I set up NextCloud on my Unraid box and have started testing Duplicati on my home computers, and those of my family to send the backups to the Unraid server using NextCloud's WebDAV protocol. (I could probably just use sftp, but I didn't want to mess with setting up all those accounts, and the other features of NextCloud will be useful as well)
Once I have collected backups for my home machines I'm looking to use Duplicati the server to send that data off to Backblaze B2. Or maybe I'll just build another Unraid box for my parents, and we'll host offsite backups for each other.