Lou,
That is exactly right, the MH gets driven thousands of miles down the highway and is subject to all of the dirt and debris that Mother Nature can throw at it. You are also right that we are not talking about a trailer queen show car, where ANY scratching from the cover is readily apparent, and this was from using one of the most expensive covers available, under ideal conditions. If a cover will scratch the paint in a temperature controlled garage, it will do the same, only worse, outside.
I am just giving my decades of experience with paint, on various vehicles. What you do with it is naturally your choice. As you say, there is risk vrs benefit. I was just commenting on the poster that says that there is no paint damage from using a cover, which is entirely false.