Try this:
medit ~/.screenlayout/single.sh and paste in:
Code:
#!/bin/sh
xrandr --output LVDS1 --mode 1024x600 --pos 0x0 --rotate normal --output VGA1 --off
lxpanelctl restart
Save, exit. Make it executable:
chmod +x  ~/.screenlayout/single.sh Open another blank file with 
medit ~/.screenlayout/dual.sh and add:
Code:
#!/bin/sh
xrandr --output LVDS1 --mode 1024x600 --pos 0x0 --rotate normal --output VGA1 --mode 1920x1080 --pos 1024x0 --rotate normal
lxpanelctl restart
Save, exit. Make it executable:
chmod +x  ~/.screenlayout/dual.shIf the output, mode, and start position don't suit you change them to something that will.
More information about your monitor capabilities are lurking behind 
xrandr --propOpen up 
arandr from the terminal.  You will be able to select your configuration.  
Add keysroke switching open: 
medit ~/.config/openbox/navigatrix-rc.xml  to keep order for humans scroll down to lines 175- 178
You will see:
Code:
  </dock>
  <keyboard>
    <chainQuitKey>C-g</chainQuitKey>
    <!-- Keybindings for desktop switching -->
Before
<keybind key="C-A-Left"> (The next line.)  Paste in:
Code:
   <keybind key="W-2">
   <action name="Execute">
   <command>sh ~/.screenlayout/dual.sh</command>
        </action>
    </keybind>
    <keybind key="W-1">
    <action name="Execute">
    <command>sh ~/.screenlayout/single.sh</command>
        </action>
    </keybind>
(This should be the right formatting.)Save and exit.  Next time you log in you can switch  with the keystroke combination of 
<Window><1> and 
<Window><2>Good luck.