I've been lurking around the forums since a few months before M&B's official release or so. Just recently in the last month I started messing around with some modding of my own, having some various coding/modelling experience and all. At first I just started doing the usual cut/paste of a few small tweaks that I really wanted in native. While doing so figuring out the workings of the module system and making note of some more ambitious changes that I would like to implement. One of those changes I made note of happened to be cdvader's outpost code.
So I've been messing with it for a bit over a week now, mostly just building the scene really and then playing with entrypoints and the cosmetic aspects of the scene. Rather than just an oupost or watchtower I went with more the true "fort" concept.
Like you, I set the fort as a new type (spt_fort in my case). I've also made a whole new mission template for the visitation so I could pretty much do whatever I wanted to with the scene. This of course breaks things like AI's knowing how to handle it but it also allows me to do whatever the hell I want with it without fighting all the default castle behavior. I keep thinking I might just go back to treating it as a castle and just hijacking the mission template when visiting to do what I want in the scene itself as that would allow the AI to recognize it without me having to do anything (I think). I'm not sure yet.
As for the scene itself, I have it setup to pick the best melee and ranged troops garrisoned and then it fills the guard slots with troops with the appropriate items. I also set it up that if you have any cavalry garrisoned that a little mounted patrol will circle the fort scene (that took me a couple days to make work right and was more painful than it should have been). Some of the infantry guards patrol the walkways on the walls. Also if you look in the middle I set up some doors so you can get inside the little tower in the middle where I moved the inventory to.
I've really spent way too much time on little cosmetic things just because I've been having fun with it. I do need to get back to coding real functionality to it. I had planned to make it siegable as well as possibly having little random bandit attacks that can occur while you're in the scene just to have some incentive to visit the scene.
I plan on releasing my version of this at some point as well but I need to finish it up and also separate the code from the other changes I've made in my little mini-mod. When I release it, anyone can use the scene if they don't want to build their own.