Server Templates / Default Script Installers

OK, I am trying to create a new template that automatically installs certain scripts upon server creation, specifically Horde (IMP), RoundCube, and Squirrelmail.

1) I tick the 'scripts below' option.
2) Select 'RoundCube' for the script.

I am stuck on what to put for the url? Ive tried
${DOM}/roundcube
http://${DOM}/roundcube
and others
and tried to save but get an error Failed to save server template : Missing or invalid URL path in row 1

What are you supposed to put here? The docs/help don't mention it at all.
In addition, how do you install IMP? I only see HORDE as an option to install and not any of its subprograms.

Thanks,
Steve