Hi Dave,
In which case I wonder if the optional auxiliary tank on the Dash-10 also had the lower section with the bladder. The structure of the wing centre-section on the Dash-10 was presumably not as beefed-up as the Series 30 and 40, which might have left more space?
A cutaway drawing would have been useful, but is (predictably) absent from my course notes and the FCOM. And one has to pay for one from Flight Global, which is fair enough I guess.
On the Dash-30, the remaining 65 tonnes capacity was allegedly in the wings only, shared between 3 tanks (one per engine, although any combination of crossfeeding was available). Presumably these 3 tanks were similar to the Dash-10's. The number 2 tank (primarily for the centre engine) was bigger, and somehow split between the left and right wings. Whether its two sides were connected merely by a pipe or something more substantial is unclear from the fuel schematic.