Like all adventures...you have to set goals and be willing to make some compromises based on design/costs. My aero cap is strictly fer learning/testing while keeping costs down as much as possible. I use hot glue to fill in the previous screw holes in the Coroplast when I have to keep it as water resistant as possible.
My current design allows me to "adjust" all the pieces since it's screwed/bolted together. Once I find the right design (fer me)...then I can move on to something more permanent and secure.
Like bondo's cap...I wanted a similar design that was very modular and could be taken apart.
The hatch is removable to allow fer taller items (like bondo's).
The hatch can be raised/locked in various positions to allow safe covered travel/camping (like bondo's)...but I don't have anything to cover the gaps when the hatch is raised...yet.
The aero cap is held securely in place with only 4 bolts through the stake pockets which would allow me to remove it fairly quickly.
My aero cap can be disassembled into 5 parts (6...if you count the cab cover)...the hatch, the 2 sides, the gap cover, and the top support...and be easily carried in the truck bed or stored in a corner of the garage.
Work with materials yer best familiar with and yer willing to sacrifice...unless yer first attempt is yer final attempt.
Be willing to accept that some designs aren't gonna work very well and learn from it.