If you are planning to smoke them at over 300 degrees water in the pan makes it hard to maintain the temperature. I typically smoke one 14 lb turkey at 250-275 with water in the pan. I add a few herbs to the water to add some flavor to the moisture. I use 3-4 chunks of a fruit wood that are roughly 2x2x4 inches. I am sure there will be several other suggestions based on the experiences of other.
Good luck and enjoy