Sharing topics was not designed for sharing whole projects and that approach will not get the files into Dropbox in the same folders. See the Rh Tour on my site.
What I would do is put the whole project into Dropbox. It is then on your local drive and that of anyone else who is going to access it. This does not permit simultaneous access, you still need source control for that. Also you have to be wary of your Dropbox and that of others being synchronized.
See www.grainge.org for RoboHelp and Authoring tips
Thanks Petar. That makes sense. I'll think about that whole-project-in-dropbox idea.