I was trying to think of a way to have a single guild fort for the entire server, something predefined but the NPCs inside might change depending on the guild who owned the fort at the time. The NPCs would wear the guild tag, and either wear the guild colors, or even draw their appearance off members of the guild.
I don't know how to create something like this without it being MoD fort itself, or only changing for the team that held MoD fort that month. Maybe you can auction it off for guild points?