Aerodynamics are the biggest factor on the highway. Not just the shape but the size combine to figure overall drag. The rolling resistance is tiny in comparison at 65 mph, and once up to speed it could weigh double and it doesn't effect mpg. The front of the camper is less then 1/2 the battle, technically the tow vehicle shields a bunch of the front anyway. I don't understand why trailer makers pay zero attention to the back where 1/2 the drag is coming from. A simple foldable trailer tail like you see now on semis would go a long way. The A/C units should be shorter and have a hollowed tapered fairing behind them that would also protect the cooling fins when backing up from tree branches. little things like the bubble above the shower on my new Palamino is actually designed well but installed backward. It should begin steep and taper slowly to the rear. Instead it starts slow and then rounds off steep, same as the vent covers on top, they are backwards aerodynamically wise. Also my new Palamino is built floor over tire with no relief for the wheel wells. Nice for the inside space but makes the whole camper sit up 8-10" higher in the wind then it needs to be. The air could go under I suppose if I were to also jack up my tow vehicle the same, but as it is a normal height truck is already cutting the wind in front at a lower level then the camper is.
The best info I have seen on this is over at ecomodder.com. What works on a Prius also works on a semi. Here is an online tool where you can see the difference between rolling resistance and drag at different speeds. Aerodynamic & rolling resistance, power & MPG calculator - EcoModder.com
It shows where your horsepower is going and what effect reduced frontal aera or better aerodynamics would have and how much is going to rolling resistance.
Oh and longer is better for aerodynamics as well, the air has a better chance to reattach after being disturbed by the poor front cap design.