Powder coatings are widely used in the automotive industry on vehicle systems, which receive years of field service. I'm quite sure that if you would decide to replace your liquid coatings with powder, you would see some very positive results. Epoxy powders are used for under carriage drive train components as well as under the hood engine compartment accessories. They also are used as a primer for improved smoothness and durability on vehicle bodies. Polyesters and acrylics are used for exterior parts such as wheels and body trim. Acrylics are the system of choice for clear-coated wheels as well as some selected car bodies.
In your case, I would choose an epoxy for the under carriage, under-the-hood parts or anything that would not see direct sunlight. A good TGIC polyester would work on the exterior color of your heavy-duty commercial vehicles. Low cure powders are available but can be difficult with handling, storage and application for the newcomers entering the world of powder. If the powder system is selected properly and the product is fully cured, your parts should have few or no defects during preassembly. One last important thing, if the metal is not properly cleaned and treated, the best powder in the world will chip and peel right off.