[bennelson]

Do you figure that the Trans Am sort of worked as a boat-tail to the RV?

Those things are so NON-aero, adding anything to the back has to help.

I am really impressed by that aero-mod pickup truck cap done by Bondo. I especially like how it can convert up for more cargo room.

I was thinking that something like that would work great for pulling a trailer.
Keep the cap down and pointy for regular travel, but pop it up when pulling a trailer to make the air flow better from the pickup to the trailer.

An "elongated" cap that had an extension to come close to the trailer might work even better, just don't make any tight turns.