This is my wiring plan.
For prototyping, I'm using the Arduino.
But there will be 10-20 magnet wires coming out the side.
To avoid that, I am planing to put an Adafruit Pro-Trinket inside, which is basically a micronized Uno. This will conceal all the wiring, except the USB. I hope the Pro Trinket will fit with all the pins in the engine section, other wise I have to place it below the bridge, which will require cutting the internal support rods. Not sure it will be sea worthy after that.
The biggest pain is actually the Micro USB cable. It is very thick, and may be difficult to fit in.
Sound components can be added any time later, but will have to remain in the base. Which is why I am avoiding the shield for this.