I cover mine after every use. It is 5 years old now and still looks new; much nicer than the one that it sits next to at the storage lot that is the same vintage. I think the Texas sun is much more harsh on things than wind/rain, so I keep mine covered. My trailer is 35' and I put it on and take it off in a little less than 30 minutes by myself.
I wouldn't waste my time/money with an Adco cover... I went through two of them in three years (I got one free under warranty). Both starting showing signs of wear almost immediately. After the second one was too torn to be useful, I bout a Carver and have been very happy with it. It is heavier, but it does a fantastic job of keeping everything nice and clean. No sun exposure, no pollen, no sap, etc, etc. Your vent caps and skylights will last much longer as well by keeping it covered.
I think everyone's first choice would be to park their trailer inside an enclosed climate controlled building... for most of us, that isn't an option (neither is building a carport, no matter how cheap they are). I think a cover protects better than a carport anyway because I get zero sun exposure.