Wood and iron have long been replaced by steel and aluminum in different types of trailer parts. Unless you want a wooden décor or interior and some premium metals or alloys for certain trailer parts, you are likely to choose steel or aluminum. Both steel and aluminum have their strengths and weaknesses. Steel is heavier than aluminum. The trade off in regards to weight is compensated by a much stronger material. Steel does not have the tendency to bend, get dented or warped and deformed like aluminum. This is not to imply that all grades of aluminum are easily bendable and can get deformed at the slightest exposure to pressure or heat.
To overcome the shortcomings of steel and aluminum, manufacturers of trailer parts have usually turned to alloys that have much more refining to achieve a better strength to weight ratio. This pursuit is driving the next phase of evolution of materials in trailer parts. Many manufacturers are experimenting with and some have also started using composites. A composite material is neither steel nor alloy. Not all manufacturers have the same recipe for composites so it is improper to be generic in this context.
Composites may very well be the future of trailer parts. They are much more flexible and yet strong. They are lighter and can easily adhere to the regulations pertaining to parts and spares used in trailers. The degree of freedom manufacturers can enjoy with composites is an additional benefit. Steel and aluminum will continue to be the two most commonly used materials and they are unlikely to fade into oblivion but we will find more parts made of composites in the near future. Customisability is another convenient reality of composites. In this day and age when people want bespoke designs, composites may be just the solution one needs.