I would mostly go along with that link - just adding a few extra points.
1. Refitting the case is optional, but if you use the bare board, either to save weight or make siting the unit easier, it is a good idea to put a wrap of tape around it to both insulate it and provide a strain relief for the wire lead. The motor can also be separated from, and rewired to the board. Already like that on some (older) servos.
2. Finding the right size wire sleeving for the drive can be tricky, the motor shaft is very short, and sleeving tends to push itself off over time, usually just as the boat goes out of reach. My preference is the flint spring from a disposable lighter. I recently got 5 for £1, picked the inevitable one that didn't work and dismembered the flint carrier. Downside is that not all designs have the same diameter spring, most have tapered ends, which can be persuaded on, and GRIP. Some are not tapered and cannot be used. There have been questions about the spring unwinding. Bearing in mind the power levels involved, nothing to worry about. The best possible arrangement would be something that fitted over, and gripped, the cog, that way there would be a positive drive and no need to remove the cog.
3. You use the pot as a center off setting control, but on a servo the deadband is very narrow, so fully off is not always easy to hit reliably. One the other hand, if you just intend to park the boat, why bother with a motor? One the other other hand (3 so far) there are robotics sites out there where circuit board mods are detailed to expand the dead band, but with my fingers and eyesight I have never bothered.