Hmm. I would think that it’s just the constants that need redefining to suit the subdirectory (you could hard code them) — FORUM_ROOT and FORUM_URL. The forum has to build client-side URLs and serverside paths (that might not map to the URL base at all), so this is not always reliable to work in a sub folder, but I’m sure it could be done, I just can’t think of it right now.