Andy. I would cheat of course (purists stop reading now please) and would take a leaf out of a crocodile I know (so as to speak).
I hate big hatch lines on things, and so I might consider making the sub as a hull, and a seperate box that slips inside the hull from the underneath, for the gear. Andy`s croc uses a little "brick" boat under the head, and he waterproofs it by the simple expedient of taping the top cover on with waterproof sellotape. How easy is that?
To expand a bit, the box could be clear acrylic, the radio antenna can be a wire out the top, perhaps with a solid wire on top to slide up into a periscope (or whatever), the motor could even be inside the box and mate up to the fixed-in- position propshaft via a ball joint. External outputs for control surfaces could be by wires via rubber bellows and quick keeper clips or something.
None of this would be seen, the bottom of the box could curve with the hull..obviously dynamic diving would be relatively easy..diving by pumped ballast tank would be tricky..but there again if you made a nice largish sub, the box idea might be EASIER..all the mechanics easy to get at and fully visible..nothing built in. I believe I may have seen slide in acrylic cylinders with all the stuff in for Boomers and so on?
See? nothing is tooo difficult !
Ashley