This is a fabulous discussion. Bt the way, I'm not the one that said you shouldn't tow an Airstream with a heavy duty pickup, an Airstream expert did. He also stated that too heavy of WDH bars will harm the Airstream trailer.
Here is the quote, "Early frame failures are usually due to grossly out of balance running gear, or, towing with a super heavy duty tow vehicle and an excessively rated hitch bars, or a combination of those."
This particular discussion came about when I mentioned frame issues. I was called out to prove it. So I did with plenty of examples.
Another example:
http://www.airforums.com/forums/f36/frame-failure-22-foot-international-48105.htm
It is nice to finally see someone admit that there were problems with certain models. The above example is a 22' model that was only 6 years old at the time of discovering the failure. The engineering didn't change on this model except for weight distribution with the layout of the traier. Think about it for a moment, (without the emotions) this trailer is a tandem axle that is only 22' long. The frame design is basically the same as most of the others, except shorter. Longer frames with more overhang will have more stress, especially if the shell is seperated from the frame. The issue is that the frame problems aren't just on the 22' models.
I must yield to folks here with more experience than me. I've only been building equipment trailers, on and off, for over 40 years. I have experience with many trailers, but I must admit, all the trailers I build had to support themselves. Understanding the semi-monocoque system, any serious failure in the connection between the frame and shell WILL cause an eventual frame failure.
Now to the axles that were mentioned above. Some folks really like the rubber torsion axles. I have used many of them over the years. They are great for a few reasons. One, they are independent. Two, they actually help support the structure as they become part of the structure. Three, they give a good ride. Four, they are cheaper to install since you don't have to deal with all the shackle brakets. If Airstream used the FlexiRide type, you could actually change the torsion angle by removing one bolt from the splines.
Now for the negative. The rubber hardens in about 20 years or so depending on the temperature. The axles don't have an "equalizer" so when you go over a large bump (usually over 6"+) the first axle will have all the weight of the trailer (that isn't on the tongue) on one axle, then the second axle. So, if you have an 8000# trailer with 1000# on the tongue, equipped with two 4000# axles, each 4000# rated axle will have 7000# on it as it goes over that sharp bump. Combine that with a marginal frame and guess what happens over time?
A leaf spring axle won't do that since it has an equalizer. There was a system that Dexter made with a split leaf spring axle that gave you an independent suspension and the equalizer, but it takes more time to build and a heavy frame to support the suspension. Another issue is some rubber torsion manufacturers will not recommend them for triple axle configurations because the lateral stress can pull the torsion arms out of the axle tube.
Like I said earlier, make an informed decision.
