I have two of the Telegizmos covers.. The main one is over a 1100 mount and previously used with my 900 mount so in use for 5 years. These sit out in the open with a 11" SCT sitting on a home made pier. I installed grommets on the covers and use heavy straps to connet to the pier so it won't flap around in heavy wind. I put a heavy towel over the scope and sharper edges to avoid wear on the covers. They sit out year round in my Michigan weather including snow (relatively light where I live) in temperatures from well below freezing to high 90s in summer. Haven' t had a bit of trouble with the arrangement and no leaks at all. I do check everything frequently for any issues but never an issue with scope or mount.
The other covers isn't left out for more than a week at a time but equally durable and of same vintage. It covers the same two mounts but with a 6" APO refractor.
The coves are rated for 24/7
for 5 years and I have no doubt they can easily meet that standard.