I use Hefty Jumbo zippered bags that have a 2.5 gallon capacity. I have used this for a 14 lb. brisket and I use it for 12 lb. turkeys without any difficulty whatsoever. What I do is take one of our pyrex cooking platters that are usually 9 - 10 inches x 15 inches and place the bag inside this dish. I place in the turkey into the bag without any difficulty. After I boil and bring the brine to room temperature, I put the brine in the bag, zip it up and place in the fridge overnight. Real simple, no igloos filled with ice, no 5 gallon containers, and does not take anymore room than what the turkey took up when it was inside the fridge sitting on a plate.
As Shakespeare wrote: "Much ado about nothing"