One of the things I've noticed is that many of the Gotha G.V are different in many ways. In some of the pictures the central storage space where the fuel tanks have been moved to show different characteristics.
In one it actually looks like the top of the original tank is protruding from the top, on others it looks like tanks were built specifically to fit within the bay.
However this is not visible on Erika in any of the available photos, so the possibility is that some G.V, Va, Vb were built using materials readily available and its possible that Erika probably had drum style fuel tanks installed. One other thing to not is the fuel model, the diagram supplied shows the model near the rear gunners position, while there is photographic evidence that shows the model just behind the pilot (G.V) and this would make sense as the last thing you'd want is a large tank of aviation fuel next to the propellers, especially as it was very common to top the fuel up just before take off.
I'm not sure when I'll be able to resurrect this project as funds are a little low having just bought my dream bike
however there is a lot I can still do in regards to the wing and engine configuration.
Manni, many thanks for thinking of me and I really appreciate it. Looking forward to seeing the photos!