You could bind mount the folder you want it to go to, into the /var/www/webdav/ folder.
mount --bind foo foo
The bind mount call attaches only (part of) a single filesystem, not possible submounts. The entire file hierarchy including submounts is attached a second place using
1: I have been using subfolder of /mnt for different things when self-hosting. Different external drives go in different subfolders of /mnt. Example: Media drives are mounted at /mnt/media, data drives at /mnt/data etc.
2: I’m lazy. Mine are located in my server users home folder. I then use scripts to sync between them between desktop and server.
3: Just make sure than your server user, the docker user and root user can all read and maybe write to them.