Reducing drag on a stunt ship is really not a governing design parameter. The difference between the total frontal area of two "typical" 60" wing span stunt ships, one with a fuselage diameter of say 6", the other with a fuselage cross section of say 2.5" x 6 " is something in the neighborhood of 5% or less. Then, when you throw in the fact that the total system drag in flight at the end of 60 to 70 foot lines, the lines represent probably more than 50% of the total drag. Besides, drag in itself is not necessarily a detrimental factor with these things because the stunt ships are really big producing drag machines. They have thick wings with airfoils that are not selected necessarily for low drag. They have a landing gear hanging out there in the wind. And then, there are those lines which are long cylinders which create almost as much drag as a flat plate with the same frontal are.
Something to think about and to keep things in perspective relative if striving for a "thin" fuselage.
Also, with carefull selection of materials, structures, internal design, and dimensions of those materials, a "fatter" fuselage can be built stronger and for no more weight than a fuselage considered to be "thin".
Hurrah for Al Rabe and his Super Semi-Scale Stunt Ships, otherwise known as SSSSS's.
Keith