Several years ago when I had my truck bed sprayed the business that did it said they had just done a trailer roof. First one they'd done. They said they thought it would work out pretty well and were talking why didn't trailer manufacturers use a similar process. Don't have any idea how it worked out.
A guy who use to work for LineX locally has a late 90s Dodge 1/2 ton truck that he's sprayed the entire body with LineX. Can't say it's the most attractive truck I've seen but he said it helps quiet road noise and doesn't get parking lot dings.