I would do Slam Specialties SS7s or SS8s in the front and Slam Specialties SS8s in the rear. Conitech does make a tripple below bag. Do you want it for the load handling?
I think I saw you on DuallyScene.com but I would also check with those guys and see what they think. There are a lot of bagged and even bodied duallys on that site!
I would definitely go with the Slam Specialties then. Since they deliver more force per PSI you can run less PSI per stroke height which makes for a softer ride.
Another big factor that determins the ride is bag placement. In the front you're limited to where you can mount the bag but in the rear a bag over bar set up will always be a softer ride than a bag over axle type one.
Please let us know if you have any other questions we can help with!