Here's how I do it.
Clay saucer w/ the bottom wrapped in foil.
Water pan with the bottom wrapped in foil.
The clay saucer in the water pan.
Then I foil the top of the clay saucer while it's in the water pan.
I change the top foil after every cook and the bottom foil once every 5 cooks or so. I have never changed the foil on the bottom of the clay saucer.

Clay saucer w/ the bottom wrapped in foil.

Water pan with the bottom wrapped in foil.

The clay saucer in the water pan.

Then I foil the top of the clay saucer while it's in the water pan.
I change the top foil after every cook and the bottom foil once every 5 cooks or so. I have never changed the foil on the bottom of the clay saucer.