How can I drag windows on Openbox without title bar?

According to this Ubuntu forums post, add the following to your rc.xml file:

Re: window dragging in openbox

I think you would want to change (or add) a mousebind entry to the Mouse section of rc.xml with a different binding. Mine currently says this:

<mousebind button="A-Left" action="Drag">
<action name="Move"/>
</mousebind>

Then you can move windows by dragging them while pressing Alt. To use the Super-drag instead use button="W-Left"

Not sure about Openbox, but most windows can be dragged by pressing the Alt key and dragging with the mouse anywhere in the window.