Rubber Roof Maintenance
Hello and welcome to the forum.
As a dealer, I have never heard that you cannot cover a trailer because of the rubber roof. In fact we have sold a lot of covers for the wintertime. However, I am talking about a cover made for the job. I did have one customer that used a blue tarp that you can buy everywhere. It got loose during the winter and the wind whipped it. When he took it off in the spring, all the moving had worn through the rubber in several places on the edges of the roof. Perhaps that is what the previous owner was talking about. If you pay for a true cover, you probably won't have problems.