Hi Mike,
I not yet faced the problem of building the main dive tank compartment, but I never saw a drawing of the structure of this zone, in any case no one useful for scratch building purpose...
I think maybe NZSnowman has some more informations on regard, but unfortunately his drawings not yet covered this sub's zone...
Maybe you'll have to imagine the missing particulars....
Cheers.
Filippo
P.S. : can you post some more photos of the second compartment that you finished, that one behind the torpedos compartment ?