Now that you mention it, the V'd front is visible in the shadow. I assume the box cavity halves swing with the door?
Given your restrictions, the opportunity is in the wheelwells and underbody. for instance the A-frame that reaches back 3-4ft under the body could be filleted on the backside. The roof vent could have a perforated metal boat tail.
http://ecomodder.com/forum/showthrea...tml#post250241
While ChazInMT was suggesting an open box boattail, I think using perforated metal would allow ventilation in and out when you're camping, but direct air flowing over the roof at speed.