Leroy,

With the bed door up, there is mostly turbulence within the volume of the bed.
Hence, protecting the surfaces form fluttering is more important than holding the fuse down.

Check this video:

http://www.youtube.com/watch?v=37R4jZJaPbE

"Right behind the cab is a low-pressure area.
As the airflow passing over the cab dissipates a bubble is formed in the bed area.
A demonstration of this would be if you've ever followed a truck with some trash blowing around in the bed and occasionally rise as if it were going to blow out of the bed, but somehow it is just suspended above the bed rails and swirls around and around then drops back into the bed and floats up the surface and swirls around some more but never blows out of the bed.
This is called the Laminar bubble.
Due to the chassis, suspension components, and rotating wheels/tires, these restriction factors, cause turbulent flow slowing down the airflow speed."