I've been been researching this subject, and have reached the conclusion that a pop-up style makes the most sense on a Ranger. Keeping the weight and cg both low is really important.
Here's an example : http://www.fourwheelcampers.com/ranger2.html
Or even one of these: http://www.adventuretrailers.com/flippac.html
would be at the top of my list.
This guy has done a nice build-out of the bed (on a Taco) for one of the Flip-Top campers. http://tacodoc.com/
One more thing I forgot to say (well, two things actually) :
With the Ranger having only a six foot bed, using a bed topper camper shell wouldn't be very practical for me, as I'm 6'-2" and couldn't stretch out to sleep.
However, one of those bed tents like the Sportz tents would work, as they include the lowered tailgate in the tent. That might actually be my first choice, as one could set up another tent to store gear in while off sightseeing in the truck, and to use as a bathroom for a portable toilet.