I think, to easily access the volman preferences, the plugin should install a desktop file that runs thunar-volman -c. A lot of user are not able to find the configure link in Thunar's advanced properties (and they are right, it's not easy to find).
Committed with revision 2761. 2007-05-20 Benedikt Meurer <benny@xfce.org> * configure.in.in, Makefile.am, thunar-volman-settings.desktop.in.in, thunar-volman-settings.in: Install .desktop file to launch the thunar-volman preferences dialog. Bug #3225.