Your trailer's black paint has faded from the exposure to UV rays and the acid washings. The original paint was applied in a very thin application by rollers and a hot dip service. It was then baked on and supplied in sheets to the trailer's manufacturer. To restore the paint's luster, involves removing the damaged surface coating, whilst exposing the better undamaged paint underneath. This can be done mechanically or chemically. There are many products that can remove the dulling oxidation. Anything that involves buffing and compounds, can result in the removal of the very thin paint coating, exposing the bare metal underneath.

I would purchase a small amount of the product and apply it in an area that is relatively indistinguishable. If it works and you're satisfied, apply more to the entire trailer. Most of these types of products will be damaged and possibly removed by acid washings. You may want to consider citrus washings instead, for a painted trailer. A communication with the Everbrite folks, may enlighten you to what they consider the best cleaning method of their products.

If the paint is badly damaged and cannot be restored to your liking with a cleaner, it may be brightened with a newly applied automotive clear coating of paint. If it's not possible to save the original paint, the trailer can be resprayed in a single or two part paint, and made to look better than new.