Subversion Externals and Typo blogs

I've been running Typo as my blog engine for some time now, and keep my blog under version control with Subversion. I have some minor modifications and configuration changes in my copy, but I strive to keep in tune with the Typo subversion trunk. So my question is: is there any way to set it up so that when I do an update that the core of my blog gets updated to the latest Typo code, but that my themes, modifications and configuration remain under my own version control? I assume there's some way to do it with svn:externals, but I'm not very experienced with that.

Originally, I had minor modifications to the core Typo code in the views to customize some HTML output which may have made this more difficult (resorting to SVK perhaps?), but now that themes can override views, I'll likely only have configuration (i.e. database.yml) and themes differing from the Typo core.