Hello, this is the 2nd version of my rc boat design that I made before. There is a shaft in my vehicle ready in the dimensions of Shaft Length: Approx. 10 cm/3.9 inches Shaft Sleeve: Approx. 5 cm/2.0 inches Shaft Diameter: Approx. 4 mm/0.15 inches.

You need to apply liquid gasket under the cover to seal it.
Screw dimensions are M3 10mm.
The hole on the back is the battery charging hole.
The rectangular space above it is the key hole. I recommend that you either waterproof the key or seal it with a bag.
The hole on the top of the vehicle is the antenna hole.
You need to insulate all of these holes with silicone.
Brushless motor as the motor.
Processor and connection type arduino nano and nrf