The reason why the upgraded shocks have external res units is to offer increased oil capacity for cooling. The metal body acts as a heat sink for the heated oil so wrapping it in vinyl would be bad during hard runs in the summer. King even had res units with fins for cooling now to help even more. If you run it hard I would not wrap them, if its a street queen most days then does not matter. But the hotter the oil the less dampening and the sooner the rebuild.