I think you are all missing an important point here.
Trailer axles, like the suspension on all cars have a built in geometry so that they track properly while traveling down a road.
If you look at a bunch of torsion bar axles sitting on a rack in some place like Prince Auto they all look bent. I recall walking by a clerk and a customer in Princess Auto one day and overhearing the customer accusing the clerk that all their axles where damaged. The clerk was a loss for words so I couldn't help but stop and explain to both of them about camber and toe-in on axles.
The principals of alignment date back some 2000 years when wagons, carts and chariots began using wheels. These principals are still in the suspension of our vehicles to this day.
I did a great deal of research into alignment principals when a friend who builds show cars and street rods asked me to design and produce a set of fabrication drawings for an independent front suspension system for street rods. There are things like caster, camber, toe-in, scrub radius, anti-dive and the Ackerman principal involved.
When I started restoring a 100 year old horse carriage years ago I had to do extensive research in to the design of wheels and alignment. Some of the info I found was in book that where almost 100 years old. The terminology was a little different (Swing) was toe-in and (Gather) was camber. Caster was not a problem because they didn't use king pins.
As far as trailers, there is only toe-in and camber involved so if you lift or drop the tounge that changes the the alignment and as a result you can have problems that the trailer will not track down the highway properly (wander) or roll easily, will cause severe scuffing on the tires
to name a few. A case in point, We only had 8,000 miles on our brand new all alum horse trailer and I noticed the outside of all 4 tires
were scuffed badly. I took it into a shop and they found the torsion bar axles had 3/8" toe-in instead of 1/8".
So the gist of this is: Keep the trailer a level and parallel possible to the ground and you will have far less problems towing.
PS The independent suspension system turned out beautify and he has used it on a number of customers street rods since doing his own.
Hope this helps