[Draco]

Now all the parts of the fuselage are cut and I'm placing the tabs and joining the subsections.

About the prominent fuel tank between the wings, it was an usual option, but not permanent. There are a lot of pictures without it, or even weirder, with a torpedor or an extra engine. This flat section, that the Stranraer had too, was used as an external cargo section. Why carry a torpedo when the plane wasn't designed to launch it, I don't know.