The slugs are the metal exposed on the coil that doesn't have the screws.
Will Boggs uses fabric tape; it's the same stuff wrapped around the pickup. Double-sticky foam tape (available at Wal-Mart) will work as well.
I'm not a big fan of silicon, mainly because it makes it hard to remove the covers later.
Just put the tape along the slugs opposite the screws on the pickup--that should be enough. I'd try it with nothing first...they may be quiet as is.
BB