A google search for box.com webdav lead me to this result:
https://community.box.com/t5/Upload-and-Download-Files-and/WebDAV-with-Box/ta-p/310
However, it looks like if they are putting WebDAV access out of order.
Basically, for any external service, have a look at their documentation, sure they point out, which endpoint to use.
Setting up the ownCloud External Storage for WebDAV is found in the admin manual: https://doc.owncloud.com/server/admin_manual/configuration/files/external_storage/webdav.html