I think the question you are dealing with is "will the Single Rear Wheel truck have suficient stability". I just pulled (for the 1st time) our new 2010 34RLSA with our SRW 2002 crew cab powerstroke on a 500 mile trip. The truck was rock solid on the road. The trailer weight and size is bigger than what I am accustomed to pulling, so I was having the same concerns as you have. There was absolutely no sway, but I had checked all tire pressures prior to departure to make sure they were full up. The 265 tires on the back of the truck and the 230 tires on the trailer were aired up to 80 psi.
I do not have air bags added, but might in the future. Your 08 truck has better suspension than mine, same rear axle and more Hp. You should be sitting "sweet".
Paul in MN