Caulks tend to be different here to silicones. The typical caulk is an acrylic based item, which is water cleanable. then you get the silicones with assorted cures and finally the urethanes with a cyanamid cure. The urethanes do shrink very little, and they tend to be compatible with copper surfaces as well, but are expensive and hard to clean up. They do make an excellent encapsulant though, at about 6 times the cost of silicones. they also take a day per millimeter to cure, so if you want to overcoat them with a hard epoxy you will need to leave the job for a week or two to cure, otherwise it will never cure once oxygen is excluded from it by the outer shell. It is slightly conductive until well cured though, like most single component sealers.