Okay, I HAVE to ask this... why is everyone writing custom installers for their campaigns, instead of someone just writing a single unified campaign manager?
Look at the Thief games. Looking Glass released their level editor (DromEd), but the games don't have any sort of "Load Mission" button... meaning the only way to load FMs (Fan Missions) was to manually juggle files back and forth... sound familiar?
So, someone in the Thief community stepped forth and wrote DarkLoader:
Basically DarkLoader allows FMs to be distributed as simple ZIP files containing all the new sound/graphics/etc directory data. When you choose to activate a mission, DarkLoader clears the way for the new mission (and even ZIPs up the moved files to save space!), then unZIPs the mission files into place.
Now why can't we have something this simple?