I suppose it depends on the age of the trailer. If it is a vintage trailer, and the clear coat is pealing anyway, then the outline of the numbers won't be the worst thing about the finish. Ultimately, the owner might strip all the clear coat and shine it up anyway, so the numbers will go away. Now, if it is a newer unit, with a milled/brushed finish and intact clear coat, then number outlines may be more distracting, and less correctable. Still not as much of an issue as hail damage or a nice scratch, in my opinion.