I have through the years followed all of the good suggestions regarding water/drip pans for indirect cookers. Boiling the water then adding to the pan, add sand then cover with foil, and recently to crumple foil then cover with foil.
I came up with a new idea that I hadn't heard anyone speak of yet. I went out today and bought two new pans, stacked them together, held them tight with clamps, drilled 3 holes for no. 10 bolts, cut copper tubing to 3/4" as spacers, and wing nuts to hold it all together to make a double pan.
The bottom pan acts as a heat shield to the top pan, where you can add boiling water or nothing at all! If you do add water to the top pan, you drastically reduce evaporation.
You can see pics on my website, address below,
You should be able to make one for yourself from the pictures and my description above!