Strip out the sound system and generator, This will save you space, money, time and battery types. It will also simplify the waterproofing of your remaining components.
I can see the point in having sound in a chuggy old diesel tug or a throaty MTB, but cannot in a steam powered ship. In my humble op' , a well managed boiler room should generate little smoke (perhaps more pertinent to oil fired boilers?) so a generator is not really needed*.
This gives you RX, steering, propulsion and pumping control.
It (Sh) happens to everyone in all hobbies. I have recently seen a sea plane hit the only tree around our pond and two inverted airboats recovered by powering them upside down to shore. They were naturally no where near as sophistacated as Poly, but everything has a value in time and material expenditure.
Recover what you can and keep us informed of how you get on. It will be a interesting tutorial on recovery and redesign. I am sure you would have wanted your pioneering exploits to be less damp though.