Thanks.
Almost finished the main hull now. I'm pleased with the gentle curves I've got at the bow and the stern just by trimming and sanding the front and rear sloping boards.
I wasn't sure if the inner ply lining the tank deck would look too thick at 4mm but I think it should be ok.
The last bits of ply I need to cut will be the floor of the tank deck and I need 2 sheets glued onto the transom (is that the right term) so I can sand the curved corners into it. Then I'll use plasticard to make the upper deck and along the sides of the tank deck, that'll make detailing easier for me.