I slapped a streamlining template on a 2007 Ford Ranger, in views #4 and 5, at the bottom right.
An aerocap, following the lines of the template in view #4, would provide a nice reduction in trailing wake. But that's nothing compared to what you'd get from teardropping the bedrails, like in view #5.
What's that? You want to load wide objects through the tailgate, and fit the wheels inside the body? Pff. I'm sure you'll figure something out.