If your trailer is not clearcoated, you can use ToolBox Polish from Lowe's to get a great shine. You clean an area, then wipe it with mineral spirits, then polish with the toolbox stuff. wipe it again with mineral spirits to clean.
If you want a very high gloss, it will take a lot of elbow grease, or you can buy polish that is coarser, and use a polisher to get it done, you finish with finer grit until you have a mirror shine.
Most use Nuvite polishes. Look these up online.