Those look great -- and with velcro seem like they'd be pretty inspectable. If you do end up with a sheet rubbing along these, the Sunbrella may not last. If you guys make them again, consider getting one of the non-acrylic fabrics that has greater resistance to wear when rubbed.
These covers can be made of chrome-tan leather with velcro and some people make a leather boot that can be slipped up the shroud
for inspection/cleaning and then brought back down over the turnbuckle.
While it is true that "out of sight is out of mind" for some people, all one has to do is be a little diligent and remove or raise (depending on design) the boot to take a look every once in a while. Oh, and to clean things.
If the turnbuckles are bronze or chrome-over-bronze or even galvanized steel
, they are quite able to deal with being covered up -- and will last LONGER if covered away from the salt
spray. Bronze turnbuckles last decades and decades w/o cracks or any problems.
On the other hand, if the turnbuckles are stainless steel
, whether covered or not they will have cracks emerge at some point so a sharp eye and constant inspection
is really needed. Dirt and moisture trapped in the dirt can lead to increased incidence of cracking. In such cases, people are often willing to deal with having the turnbuckles be exposed just so they are constantly inspectable. Of course, just because they're right in front of someone's nose, doesn't mean that person will actually see the cracks.