Using the water pan to catch drippings to make gravy is a no-go, they will burn. Drippings burn on my water pan even when I have it covered in foil. A second pan on the lower rack may work, but it also might get to hot with the long smokes. I would try a doubled up pan, or a smaller pan in a larger one ( kind of like a double boiler ) to add a little more air / heat deflection.
I usually just go with a pan of beans to catch my drippings in.