Tires on tow vehicles have very deep tread when new. These tires will not only give you great tractions, avoid tire punctures on gravel roads but will also pick up stones. These stones and lodged between the treads until... you reenter the paved roads and gain highway speeds. The centrifugal 'force' of the rotation of the tires to release these 'projectiles' INTO your trailer in tow.
I searched on Google: Solar Stone Guard - Wrap Protectors and was able to pick one site that covers all of your questions as to what Intermountain Airstream Supply call Segment Protectors. Prices and what fits which models.
There are other sites to visit, as well.
When discussing Trailer wheels and tires... I thought this appropriate for Running Gear' Tires.
Do not expect these Wrap Protectors to fit... perfectly. They do not. Even on a factory installed set, they are a bit irregular in fit. From a distance no one would notice, but if you are opening and having the Stone Guard hinge on the inside to clean behind the panel... you will understand. Stones can be caught and drop in between the Wrap Protector and the vibration of the road will grind the stone into your trailer's aluminum panel. I will swing my panels open to drop loose stones trapped in between the trailer and guard.
The bottom curved edge widths from the trailer's aluminum skin can vary from 3/8" to 1/16" depending on.... ?.
Even an adhesive durable plastic or one that can be screwed onto the frame members would be better than nothing.
After eight years towing our 23 foot Safari in the Rocky Mountains the dings in the stainless steel were beyond counting the impacts. It is an investment, versus enhancing the appearance of your trailer. They look a bit awkward, but a very positive awkward.
Although the internet reference is a commercial reseller of hardware to Airstream owners... it is the FIRST step of gaining an education of protecting your investment in your Airstream trailer.
I am disappointed that Airstream does not attache these panels on ALL MODELS as standard equipment... but there is more money to be made selling you a trailer in separate parts. Just a fact of doing business and negotiating with the RV Dealer you make your purchase.