The shocks supposedly dampen the oscillations of the axle, much like the springs on your car. There has been some debate on their effectiveness and in fact some of the newer model Airstreams don't even have them. The rubberset rod in a tube Duratorque axles do behave differently than your usual leaf and coil spring suspensions so that may be the reason for the difference in opinions. If you have them original from the factory you might as well keep them. They aren't too bad to change, but there can be some interference with reattaching the new ones due to their bolting locations close proximity to the frame. Usually a bit of coaching with a pry bar will get you enough clearance to get the new one on. The old ones had split rubber bushings which made them easier to replace but no more, solid rubber seems to be the norm. They are also a special application due the almost horizontal position and require special internal valving.
Good Luck my friend!!