hi,
As far as I am concerned, If you want to share sensitive work, I'd sign a nda. I almost only working under these conditions anyway.
I think you should actually set up a small group on google for example and open on this forum a thread to join this group, that would work I think, because who would be responsible for selecting members? that would not be a very objective way, some people with not a lot of activities on this forum can ( and most likely are in many cases) be far more knowledgeable and experienced than very active members, so on what bases would someone define who can be part of this group better than the owner of that particular project.
Bye,
Jean