We had a cover and it was big and heavy to get on the coack, I didn't get it tied down good and it worked against something on the roof and the wind split it in half! We decided we used it often enough that we wouldn't buy another.
We are usually out at least every other month so it got left in the garage more than on the rig to start with.
Even with it ripping we did not get any damage to the coach. Modern covers breathe so they don't have the mildew and funky problems of old. Those problems are more often caused these days by plastic tarps over the cover or just over the rig itself.