I've trailered thousands of miles over the years and have never suffered any hull damage.
However, you can and will find lots of grease at times on the hull.
I'd worry more of having flats!!
I once had two tires blow out on the same trip.... not good when one has only one spare and is right in the middle of Alabama....... As said to me; "Everyone knows, everything closes at 12:00 on Saturday in Alabama" It was 12:10 when the second tire decided to blow!! Trust me NOT everyone knew everything closed at 12:00 noon on Saturday.....
