regarding real world aero effects on fuel mileage. I tow this box shaped camper I am in right now ( funfinder 189 FDS ) ....7 feet wide, 10 feet tall, 19 feet long including tongue. Sloped back front, the rest of it sq edges, with my Nissan Frontier. Overall fuel average over approx 25K miles has been right at 11.4 mpg.
I also tow a two horse trailer with this truck. Lower roof height ( whole trailer is lower to the ground due to torsion axles, and wheels being set outside the box. Rounded front end, rounded corners similar to an Airstream design ( except the back, which is square ). Approx same weight as the camper. I get approx 1.5 mpg more pulling the horse trailer with same truck, same speeds.