Advice on custom app with blogging interface

I am developing a custom app for a local company that needs to handle a lot of customer specific actions. However, they also want a blog that is somewhat tightly integrated into the app, for instance when a customer logs in, he will see items he can take action on, but also can see some of the “news” from the blog.

This blog should also support RSS and atom feeds.

My question is this:
Should I try to piggyback on one of the current rails CMS systems, (i.e. Radiant, Mephisto, etc) or just build my own? I read a post recently about how RSS is very easy to do in edge rails, which is what I will be targeting since by the time the app is released rails 1.2 will definitely be available. Also, the Radiant source code is available under the MIT license, so I would be pretty much free to borrow whatever I needed from it. I guess my main concern boils down to whether or not developing a small custom blog would be too time-consuming, and also if by not using a mainstream CMS I miss out on easy updates/security fixes when they release new versions.

Any thoughts on the issue would be appreciated.
Thanks,
Tyler Prete