I have air helper springs on the back of my class C. They definitely help the handling some, preventing some wallowing around (for lack of a better description), but don't prevent transients from reaching the coach. They mainly just increase the spring strength.
Replacement shocks can certainly help some. I would suggest seeing if Koni FSDs are available for your chassis. They are not inexpensive, but work nicely, and have special valving that varies the stiffness based on the speed of the motion (so they give good damping for big bumps but are not rock hard for little ones).
As was said, proper tire inflation can make a big difference as well. Also, if you have any play in suspension bushings, those clattering around can also exacerbate things. At the end of the day, though, a gas motorhome is not going to ride like a Cadillac or an air-suspension diesel pusher.