[hat_man]

Sounds like a neat project. If you cut on the green lines and remove the upper section (I'm pretty sure it's taller than the cab) that would help quite a bit. I can't tell if it's the angle of the picture or not but if the height at the cab (red line at cab end) is taller than the red line at the rear it would give you a slight downward slope. Not the optimum 12ish degrees but better than an open bed. you would also be able to keep the windows and tailgate window intact.