Les - The Gen II bed has indentations to use a 2X4 board as a divider. It's open at the top, so you could use a 2x10 or wider too. Put some truck bed paint on it, and it can look pretty sharp and be very useful.
Edit - BTW, I keep my extender in the bed. My biggest headache with it is loading large objects. I wish it had a mechanism to hold it in an upright position so you could load with it up out of the way. I can balance it, but the first time something bumps too hard, it falls over. I use bungee cords to hold it up right now.