Years ago there were some gaskets to avoid. They were molded with a lip that faced upward and they caught and harbored water. Not so bad if you lived out west where there was not much humidity but otherwise they'd make the base of your mirror rust. If you have any or if you have a plumber friend, shower pan liner is good to use. It is some of the toughest stuff you can find and is made from a PVC compound. You can use any common vinyl spray to make it black and a friend uses a permanent Marks-A-Lot to do this, also. If you run out of possibilities, let me know and I'll mail you a bit of it.
