Many of us are convinced you don't need shocks. Torsion axles provide their own damping. Airstream may install shocks just because people expect them.
I took great pains to get the shocks perfect when I replaced the axle on my Caravel
, but I didn't even put shocks on the Overlander when it got new axles. I've made two 3,500+ mile trips since then and it tows great. I don't see any significant difference--items left on the top of the table tend to stay there. Occasionally a very big bump might cause an extra porpoise cycle, but it takes an exceptional bump to do that. I think the rig would porpoise even with shocks.