Most teardrop trailers are LESS aerodynamic than you would think, but they are still a giant step better than the typical big n boxy trailers other people use.
I think the trailer probably has more of an impact than the load in the bed. The trailer is about 900 lbs AND has two wheels on the ground, so besides wind-resistance, it has rolling resistance as well.
The load in the bed is just weight and almost fills in the space behind the cab, so I think that it doesn't have too bad of wind resistance.
I ran into THIS trailer at an event a few years back, and the owner claimed to get better fuel economy with it than without. If I recall correctly, the trailer was fairly light and the truck was a Dodge Dakota with a cap on it. You can see the slant on the back of this trailer is less than the curve on many teardrops.
