Diplostrat,
You are one of the most knowledgable and articulate people on here. I perused your website and enjoyed reading about your colorful life . Without speaking CAR-ease, you are speaking my language. I too was one of the 'first world jeepers' who obsessed about torsional issues with a wood frame Lance truck camper well strapped down to my short bed truck. I have now come all the way around to your thinking, which is a light, short bed camper box on a Chevy or Dodge one ton platform has very little torsional issues. Besides adjusting the tie down torque to fit the situation; loosening the rears when I think the frame is going to twist, I don't need much adjusting. Here is a pic at near maximum axle twisting: very little change in the attitude of the 'box', i.e. very little frame twist, and no damage which has been widely predicted:
Ford platforms with their penchant for frame twisting needs extra help to keep the twisting frame from pulling the camper box apart.
Here is a short vid of my ride up the Diablo Drop Off, a 100m blow sand dune with my current setup: 20 pounds of air in tires; started in 4th gear/low range, downshifting to 2nd gear/low range for the deep moguls near the top. The front/rear True Trac differentials were superb and transparent in delivering power to the wheels with traction, not the other way around, even with a wheel off the ground.
https://www.dropbox.com/s/bfj5y93wsd7vfkw/jefe does sand hill at dry wash of the devil Anza.m4v?dl=0
In a long bed format, the 'pull out' springs at the front or rear, not both, of the bed would help mitigate the stress. US military trucks from the 1950's on use this method. All the heavy camper boxes above, by shear weight and length of frame have twisting, some models massively so, that have been or need to be addressed usually by the manufacturer.
The washboard issue of which you speak is alive and well in the Desert Southwest, U.S. I've been on thousands of miles of washboard and use the air down method to allow the tires to take more of the suspension's job and kill the bad vibes. My brother, who won the 1st King of the Hammers off-road race in California believes the secret to washboard road running is to air down and go faster, not slower, kind of like the lifting of a power boat at speed. Running at much lower pressure we had a couple long, straight, horrible sand based washboard roads in Death Valley that we traveled @ 100kph in a pair of 4.5Kg rigs to good avail with a hanging dust cloud as far as the eye could see. I followed him @ 10km distance.
jefe de doble traccion.
