Great progress so far!
The gaps/joint might not be as bad as they seam (see what I did there? )
If I may suggest, finish the assembly of the block around the main mast (above the hangar) before you start filling.
Then, instead of putty, use a medium CA applied with a toothpick or other sharp tool and use silver paint to check it’s coverage after curing for the seams on the superstructure.
This way you get a much more accurate “fill” and the resulting material is not as soft as putty and will sand to a nice crisp corner much more easily. Re-apply silver paint after sanding to check the shape and to determine if you need to add any more CA.
For any seam line on the hull, though, stick with putty as you need the coverage and of course its softness to sand in the organic shape
Hope this helps