Lots of places on the fuselage have cosmetic issues. This is the top of the fuselage. As you can see, I used a fair amount of filler here, although most of it will be sanded off. It's a bit hard to tell, but there is a seam down the middle of the fuselage as apparently the exterior portion was molded in two halves, right and left, and joined in the middle. This seam is not even, and has a bit of a cavity to it. That's the main area that I am filling.
The three blue-colored holes in the foreground are where various items will pass from the fuselage to the wings (the wings attach to the top of the fuselage in this area) such as rudder cables. The blue is simply painting/masking tape that I applied from the inside to close off these holes and prevent interior contamination when spray painting the exterior.
The two oval white "plugs" are simple cardboard with blue-tape-handles that I am using to close off the intake scoops. Those scoops lead directly to the previously Zolatone painted area of the fuselage interior, so I am plugging them with the cardboard to prevent the exterior spray painting from contaminating the interior.
