Couple of things. When I was hauling a new bike home from NC to MI many years ago, I was informed to never cover it when hauled. It will rub the paint right off. Seen it on other bikes.
The paint, if like mine, is automotive grade, clear coated. Just like your car. It will protect, but you need to treat it like your cars paint.
Finally, Dicor reps/engineers were at the Coachmen rally in 2014. They recommended NO covers for trailers. Their opinion was that if you just take care of the roof, no cover is needed. Also, they noted that many people incorrectly install covers, often too tight, damaging the edges and corners of the roof. In other words they can cause more problems than they solve.
A fixed solid roof is a better solution. Wish I had one. But I put mine in covered storage over the winter.
2011 Brookstone 354TS
2013 F350 SC 6.7 DRW