Sort of off topic but I wonder if the SRT10 short spoiler on the longbed would help aero by giving a landing pad for the air coming off the roof right there. It's about right where the template line is at the tailgate in your drawing. Same thing with the taller Daytona spoiler on the short bed, about 8" high at the tailgate would be about right. If nothing else might be a good platform to build the rear of an aerocap on.
The short one might even turn around backwards and mount.
PS, the 2002-2005 Ram is the best looking truck they ever made IMO.