[shovel]

Just going on what I've learned from reading + hobby experimentation, I'm going to guess the oldschool trailer is going to be the more efficient one. It's significantly lighter, draws a significantly smaller wake than the "aero" one, and isn't significantly less aero in the rear at all.

Up front the biggest improvement would come from closing the gap between the van & the trailer, as has been mentioned. Might be feasible to attach a "bulb" to the front of the trailer with its midpoint around the roof height of the tow vehicle, extra storage for tarps or muddy boots and at the same time closing the gap a little & providing a bit of radius for air passing to the sides of the trailer.