Got as far as marking up the first rib, then I had to quit for the night. In the meantime, I have some pictures of the frame base.
The idea for the frame is to allow a rapid initial construction and installation, while giving enough space and material to install an articulated hinge in the near future. The idea behind using an articulated hinge is so that, while the entire aerocap moves rearward and up, the aerocap will also tilt so that the rear raises up, and the aerocap front will avoid contact with the rear of the truck cab. The entire aerocap will be able to move up and out of the way enough to provide useful access to the truck bed.
The aerocap will eventually use the latch provided with the existing tonneau cover, to latch the cap shut.