Thanks for all the advises!
I will get going with the calculations of upper structure volume/mass.
The sheet steel is an interesting solution, but unfortunately I don't posses any experience..
Which me and a friend do have, when it comes to epoxy laminate and carbon fibre (which I wont use but similar process).
I'm leaning towards some type of epoxy laminate for the structure above waterline.
With "plugs" and molds. A bit time consuming, but worth it.
Probably epoxy laminate for the aft and stern sections too.
Will get going with the molding in the weekend, primarily the aft and stern.
Awaiting an order from engel-modellbau with rubber bellows and u-joint couplings. When it arrives, I will be able to finish the "end-cap" and then do some water testing. Either reuse the old rc-kit from the old submarine or buy a new one for the testing.
Have a great weekend!
Cheers