Have you tried Arandr? It's a GUI front end to xrandr that gives you both
drag and drop monitor manipulation and a command line that you can use to
write your own scripts. I use it with Enlightenment, on Debian and GNewSense
but I see that it's also packaged for Trisquel. I've also used Krandrtray
and a much older version of Gnome's randr front end and, and have probably
done so with Window Maker, so I'm not sure why this is not working for you.
The only thing that's tricky about Arandr, and GUI managers in general, is
that you have to drag a monitor around to see the second monitor under it.
Arandr starts up with the two monitors in the same place so one might hide
the other. Krandrtray does not have this problem but you have to right click
your way into things to activate the external screen.
A prior forum post,
https://trisquel.info/en/forum/adding-3rd-monitor
A page with links to some of my own use of external monitors,
http://50.81.205.197/photo_album/chron/desktop/external_monitors.html
I'd like to see some screenshots of your success or failure. Best wishes and
happy hacking.
