Can I set up a direct collaboration between two tenants

Hi Jim, 

Welcome to Box Community and glad to assist! 

You can share your contents without merging your accounts by sending an invitation to collaborate on your folders. 

 To invite someone to collaborate in a file or folder:

1. Open the Share window. To do this, in your Box files view, hover over the row of the file or folder you wish to share.
2. On the right, click Share.
   
   
3. The Share window opens.
   
   
4. In the Share window, under Invite People, click Add names or email addresses.
5. Type a collaborator's name or email address.
   • As you type, Box anticipates your intended recipient and lists corresponding email addresses.  You can select the recipient you want, or continue typing the full email address.
   • When typing full email addresses, separate recipients by a horizontal space.
6. Click the Invite as drop-down menu. Box displays a list of roles.
7. Click the role you wish to assign to the collaborator.
8. (Optional) In the Message field, type a message of up to 750 characters for the collaborator.
9. Click Send.

To know more, please visit this article. 

Thanks for posting!