Are you using Basecamp as your primary communication management channel inside your company? Is your partnering firm using Huddle for the same purposes?
Did you ever have any problems with the transferring of documents? Do you think that it would be easier to bring Basecamp and Huddle together?
The Pontibus Basecamp - Huddle connector is build to connect your businesses. It helps with sharing documents from Basecamp to Huddle.
Once you do this, the updating of the documents will be much easier.