Whomever you get to paint your trailer, will probably have a particular brand which he favours. It will depend on his local source, and what he is used to using. Most automotive urethane brands will work well; there are several. Because you want a silver colour, which contains metallic additives, few "tractor" paints will be applicable or available. The metallics are usually over coated with a final clear coating.

I would discuss this matter with the person who will be doing the work for you. He will know what is involved in the preparation, paint compatibility, and desired finish. His choices of materials will differ, depending on if your trailer is steel or aluminum. The type of paint will differ depending on if you select a single part paint or two part colour/clear coat. Your budget may be a deciding factor.

There are many variables, too many to list here.

Gard