We use Basecamp 3 to manage our day to day work.
A Basecamp project space is the place to look for all of the resources relevant to a project. All tasks should appear in there, all documents should be referenced in there. Typically documents are stored in Google Drive and Basecamp holds a link to the document.
All core team members have access to all Basecamp project spaces.
All associates have full access to the relevant Basecamp project space for any projects they are involved in.
People from clients will often have full access to the relevant Basecamp Project space for projects they are involved in. Some clients have more limited access (typically this happens in support contracts where clients don't want to see the detail of our working).