You have some great ideas, GreenAce. Regarding your question on a diveable sub, typical r/c design is the cylinder you're
talking about--plus a hull around it (that's "wet hull" construction). The idea kind of mimics the subs at least of WWII
that, having flat topside decks, had free-flood areas under the deck and other places. I don't think nukes have as many
because, around WWII, free-flood areas, with rows of holes, were found to cause considerable noise and make a sub easier to
detect. Wet hull r/c sub construction also vaguely mimics navy subs' ballast-tank placement; while not free-flood areas
because they hold onto a set quantity of water, I think nowadays still navy subs' MBTs (main ballast tanks)are
designed open at the bottom.

I think whether you can salvage a Seawolf for such a design depends on whether you can find small enough r/c board or boards.
I won't try to convert my Revell Skipjack 1/230 unless I find a board that can be rolled up like a tortilla.! But the
Wally Seawolf is nice and fat for a footlong sub; I think equipment I've seen in my local hobby shop would fit it.

About waterproofing the chips...I would only attempt that as an experiment to see how long before trapped heat burned up
transistors or melted the sealant.

About sealing moving parts...only prop shaft, in my case...look at your salvaged r/c sub motors , where the shaft for
forward drive enters the detachable end of the motor housing (not the wired end). If you unscrew that plastic part from
the clear motor housing, you find a little pot of goo: silicone grease. That's called the stuffing box.

Notice:
1. the opening in the front and back of the box are exactly sized to the prop shaft to keep out water with nice, rigid
parts.
2. where the plastic part can't be sized to the prop within a tolerance of microns, the silicone grease is used because
it can be pushed by water pressure to seal the inner prop shaft opening tighter; but the grease is thick enough it won't
fill up your motor casing. A little water may still get through atomized, but...oh well ! It's slow enough you can clean
that casing out every few runs if you're careful to seal it up well when you put it back.
3. I've read submarines tend to have that disc you see in the stuffing box, that annular ring with the shaft through it.
I guess the idea is water, when it fills the end of the stuffing box, smooshes the ring onto the grease evenly, improving
the seal as the sub encounters increasing water pressure.