I have put axles on 2 separate Airstream trailers. Airstream originally used a 22 1/2 degree down angle axle made by Henshen. They were bought out Al-Ko. Axis Axle also make the torsion axles.
When I replaced axles I used the Dexter 32 1/2" degree down angle because this gives about 1. 5" of lift over stock which is good for ground clearance and modern TOO TALL tow vehicles. Torsion axles have been used on Airstreams since the mid 1960's. In general they can last up to 30 years but that is by folks use them frequently. If a torsion axle sits idle then they go bad. I take the weight off the axles during the off camping season.
When Airstream calculated the axle weights, both axles together would equal 90% of the GVW.
If you look at a slightly older Airstream they can be found for a decent price if you look hard enough. Like all RV's there are pros and cons to each manufacturer. I own a 1994 Airstream 30' and absolutely love it!
Actually the original Airstream torsion axle design was Airstream's and the axles were originally built by Airstream in their plant. In the early '80s, I think, when Airstream was in financial trouble and was purchased by a food processing company whose name I can't recall now, the torsion axle department and designs were sold off to Henschen who was located in Jackson Center also. Henschen built the axles for a number of years. I haven't owned an Airstream in a few years but I have toured the Airstream plant in Jackson Center several times and also visited the Henschen plant in the '90s. I didn't know Henschen had sold out.