Figured out a way do to my gap cover. I will have to move the front support bar on the hatch back behind the front attachment bolts...which will be about 6". I will also end up trimming about 2½" from the front of the hatch so I can put in shaped bar fer the gap cover. This will allow the test cover (Coroplast) to keep it's shape and allow me to put in a vertical guide point. The guide points will be a bolt that will allow the gap cover to rise just enough to allow clearance fer the cab cover and pivot when the truck flexes.
I envision the bungee cord attached to the cover at 4 points (2 points per side) so it's a "V" shape and attached to a bar below. This bar will allow me to remove the tension with one hand and to open the gap cover from either side (driver or passenger) to deploy the cab cover. The bungee cord will provide enough dynamic tension (when adjusted properly) to keep it in contact with the cab and aero cap. A thin rubber weather strip located under the front edge of the gap cover should provide a seal against water leaking past the gap cover and down the back window.
It's gonna be fun to match the right curvature fer the gap cover to the cab/aero cap.