Some materials can survive harsh UV rays and severe weather, others not so much. 20-30 year warranty is useless if the trim, fasteners, or sealant fail before that. Which they will.
I began covering my trailer with an Anco cover, and will continue to do so.
For 6 months of the year, why leave it exposed to the elements if I have a choice?
And uncovering the unit in Spring, results in the same clean unit I left in Fall. No junk piled on. No sap. No dirt. No bird poop. Nothing.
The down side is that you have to climb on the roof. I do it myself and it takes about 30-45 minutes all said and done. But its risky being up there moving all around with tripping hazards all around.
So, is it really worth it? Only you can decide.