I have air bags with a Viair 10007 onboard air system. I always thought that airbags were not needed if you had a dually. Wrong! lots fo people have them on everything from half tons to 450 series trucks. I was pleasantly surprised when I added them to my dually. Even though my pin weight is around 3000 pounds, the truck would sometimes porpoise really bad on the interstates. Now at just the touch of a button, I can stop that! Run them at about 12psi when empty(actually rides better now) and then about 30-35 when loaded. Plus, I put an air chuck under the side of my truck so I have air available for tires, floats or what have you. Never had Timbrens, just bags. Won't tow heavy again without them.
2012 Sandpiper 365SAQ weighing @ 15k, Onan, 2nd air, slide toppers, TST
2013 F350 6.7L Lariat 4x4 CC DRW,Viair 1007, Ride-Rites, Edge CTS, B&W
2001 Chevy 3500CC DRW 4x4, 8.1L, 4.10 gears w/ Detroit TrueTrac
2001 Ford Excursion Limited 4x4 7.3L,V/B Spring Mod, ProComps, Hellwig Swaybar, & other 'Necessities'