I've not observed excess corrosion under even tight plastic. I prefer slightly loose tubing so the lines can roll over the shroud but this, like the even nicer wood rollers, may seem to some excess windage and to others clunky looking.
Shrouds generally go at a fitting, where the wire has been stressed and salts can accumulate with moisture.
While on covers and to vent a pet peave: For stainless and bronze turnbuckles, I hate turnbuckle boots and hate tape even more. A properly installed turnbuckle with properly sized cotters and clevises leaves no sharp protrusions, especially if one uses Brion's trick with the welding rod in the turnbuckle studs.
For galvi or iron turnbuckles, there's nothing like a nicely fitted sewn leather boot that's packed with lanolin or even waterpump grease.
G'luck
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