You can install proxmox on a minimal debian install. That way you can set the disks up the way you like. I think setting up omv in an lxd container would work but I wouldn't do it that way. If you try and it works fine let us know.
I use zfs mirrors for important data. Remember mirrors are not backups.
Thanks for the suggestions and info. I'll hopefully have time over the weekend to give it a go. If I manage it I'll update here