We live in Michigan, and I have used an Adco cover for all the years we've had a travel trailer (which is 9 years). Our first cover lasted 6 years, after which a bought a new one. When I sold my camper this spring, the cover was still in good shape.
Up here, we can use our camper about 6 months of the year, the other 6 months it is covered. As in other comments, you have to protect all the corners with something soft. I've used old towels or rags. The idea of using swim noodles is also a good one. The covers do breathe, but there will still be a little bit of mildew under the cover when you take it off. Nothing a good wash job will take care of.
The advantage of the cover is to keep the UV rays from attacking you RV. In 9 years of owning our camper, it nearly looked brand new when we sold it.
We plan to buy one for our new Montana High Country.
Noteworthy: Our 2nd Adco cover was WAY better than the first one. The strapping is improved, as well as the UV material. If you take care of it, and protect the corners, you should get several years of use out of it before it deteriorates.