The UI is most definitely a work in progress. There are things it does wrong.
Try this one: http://agcl.us/cltc-configurator/; it's not quite as up-to-date as the version in GitHub for Roadster (my updated version of Smoothwall), but it should let you create a workable config. It starts with a default scheme that should serve as a guiding example. Remember to save both the scheme and the generated script. The script should work on most modern Linux platforms.
I have another version, http://agcl.us/traffic_control, that is better integrated with Smoothwall/Roadster, but the scripts it generates will require a little tweaking to work with generic Linux distros. And you have to start from scratch.