At the moment google indexes about 12 pages, eg homepage, terms an conditions, FAQs page etc. All the pages that anyone can read.
Can i open it up so google indexed all pages, but still be behind a login wall? So can you feed google just the meta title and a description that maybe takes the first 160 characters from the OP? Might this be enough for it to get indexed, then a user clicks on it and they then have to join the forum.
Or is this a bit sneaky and google just won't index it as it's not great for the user as there is no content on the actual page, unless they join the forum.