I know my FLD120 & now my M2 both have rear sway bars.
On my FLD120 we added front air bags to the rear of the 12,500 lb front springs and that gave a great ride, but also increased the side to side motion. On my M2 with 14,600 lb front axle I do not have front air and it is real stable, with only slight rougher ride. It actually is not enough of a difference to put the air ride on this truck.
2012 Showhauler 28'6" Motorhome on a Columbia w/ 450 Mercedes.