Do I neeed it the air bag helper suspension.......

Don't see any problem with your truck's rear sagging a couple of inches to level. If your headlights are pointing up to become blinding or non functional then maybe bags. If your 5er is level and your truck is level then you are in good shape. Air bags won't improve your ride much. An air hitch or air pin box will. Sounds like you are already happy with your tow.

I installed air bags on my dually and have yet to use them; I have less truck and less trailer.