Openbox is written as a complete Window Manager. By complete, i mean, full of "capabilities". However, in a DE, other tools tend to provide some of the "capabilities" that a full featured wm offers. So, i think a better aproach would be Oroborus, a simple and light wm, with the bare minimum, and theme support :D.

I've already talked about that here: http://forum.lxde.org/viewtopic.php?f=4&t=1762