Wayne,
We have 18" Cooper Discoverer A/T3's on Jeanie's '11 Jeep Grand Cherokee Limited as winter tires. They work well and were very quiet at the beginning, a huge selling point for us. Since we've had no winter the last couple years we just leave them on. The tread wear seems very slow. The only thing I do not like about them is the increasing tread noise. They are getting much louder with age. I was thinking about getting them for the TC, but the noise thing throws me off. Plus, in your case, they have a wide carcass which you may not want with duals.
I noticed a generally lower load rating of 17" tires compared to 16" tires. Maybe this does not matter with a dually as you can spread around the load on 6 tires. If no off-road is in your future, you might look at some of the skinnier, high miler truck tires to keep more space between the duals and have a longer lasting tread.
jefe