Persistent configuration of two screens

I want to configure two screens side by side and want the configuration to persist a system restart. (I'm using xfce on Xubuntu 12.)

I've inspected old questions and the answers mentioned arandr and xrandr, and so I did create the (working) shell script that calls xrandr with appropriate options and arguments to fit my needs. Now I can place that script in some profile so that it will become active with every login.

My question is; is it possible to configure twin-screens in some system config file so that I need not have a xrandr based script executed each time?

As far as my investigation goes, the config file could be /etc/X11/xorg.conf, and the file contains sensible information for my twin-screen setup. But that configuration seems to be ignored.