The finish coat is the next to the last layer of protection for metal. Paste wax or TC-11 is the final layer of protection.
Finish coats have a very high affinity for the primer, and they are very weather resistant. There is no such thing as weatherproof paint: a finish coat always fails, it is just a matter of how long it takes. If the finish coat is properly maintained, this can take decades and if conditions are "just right", centuries.
In the case of equipment that is treated with TC-11, alkyd enamels are the paint of choice. They are durable, flexible, weather resistant, and 100% compatible with TC-11. This type of paint is often packaged as engine enamel. It dries quickly, and is an easy paint to work with.
Make a concerted effort to purchase the finish coat form the same manufacturer that provided the primer. Some finish coats and primers are completely incompatible,
Do not apply paint of the humidity if over 90% or rain is predicted. The relative humidity goes up to 100% when it rains, which means that the dew point is the same as the air temperature. This means that the surface will have a film of water on it, even if the rain does not impinge directly upon the surface. he water ends up leaving a void in the paint, and the paint with this fault may fail more quickly that a paint job suffering from vapor entrapment.
Pay close attention to the temperature. Paint manufacturers provide a range of suitable temperatures. The normal range is 60 to 90 F. If the surface is to cold the solvent will not evaporate quickly enough. If the temperature is too high, the solvent will evaporate too quickly. Either phenomenon results in low film strength.
Let the primer dry completely before the finish coat is applied. If the primer is not completely dry, the paint will suffer from vapor entrapment, which means that solvents that are not supposed to be in the primer are in the primer. The result is that the primer never gets hard. If the paint rusts within a year of application or comes off easily with a fingernail, it is probably suffering from vapor entrapment.
It is not unusual to have both conditions at the same time in the construction industry, i.e. the temperature and the humidity are not within the acceptable limits. Contractors are usually in a big hurry to get the painting done, and they will paint in any condition.
Boats, automobiles, and aircraft have spectacular paint jobs when they leave the factory. The finish coat on a production automobile is an engineering and artistic masterpiece, and the company has to spend millions of dollars to have the equipment to do it properly. Ironically, most of the automotive paint jobs fail because the owner doesn't want to spend ten dollars a year on paste wax and two hours working on their car.
It is a good practice to apply two coats of finish paint. This takes care of any missed spots, thin areas, and requires a minimal additional effort.
If you are applying the final coat of finish paint and you have taped off areas, remove the tape when the paint is wet. If you wait until the paint is dry, you will chip the paint when you remove the tape.