If you could do an inter-library loan for one of Wolf Heinrich Hucho's books on 'Aerodynamics of Road Vehicles',you'd find a wealth of empirical data from testing of commercial vehicles of all kinds.
There's a lot of quanta.You could noodle various configurations,look at the numbers,see if you can get close to your target.
The Renault V.I.R.A.G.E.S. tractor trailer is Cd 0.29 with extended boat-tail.
Fluids is fluids.University-built 7,000 mpg student projects,or World Solar Challenge aerodynamic technology can all benefit a truck/trailer.
You've mentioned some good ideas.GOOGLE IMAGES is your friend!
Will wait for your sketches.
