Jo Ann,
Axle skids on Airstreams as delivered varied by the axle manufacture,
model of axle and year. There were at least 3 manufacturers I know of.
On the 1950's HADCO hydraulic brake axle, there were skids:
http://vintageairstream.com/floyd/brakes/brakes.html
(mid page)
Yet the axle on the Bubble there wasn't:
http://vintageairstream.com/archives1/%2757BubbleOI-1100dfs.jpg
Body mounted skids started appearing on single axle trailers with the
Dura-Torque axle in 1961 - but not all. Doesn't show up in the option
lists, yet many of the installs I've seen are original - including the
ones on our '65. They appear in the owners manual in the side view. As
for their effectivity - as Fred Coldwell noted - I believe in them after
out axle broke. Once the tire folded up in to the wheelwell, the skid
took the weight of the trailer - otherwise it may have tumbled the wheel
out of the wheelwell - causing further damage.
You can discern the body skids in the first picture on this page:
http://vintageairstream.com/myrtle_tour_b4.html
Best of luck,
RJ