Ok, now I'm not a mechanical, but I am a climber and an engineer. First of all climbing slings are tested for blunt holding force, 22 kN is 5000 lbs, remember F=ma. Climbing ropes are meant to stretch, but only when there is sufficient length of rope extended to absorb the force, small parts or a rope have very little absorption capability. So, what is the problem? The system is only as good as the weakest link. If you make the turnbuckles rock solid then the camper connection or the truck bed is the next thing to blow, and that can be expensive. So, what is needed is something to absorb the instantaneous force and dissipate some of the peak energy (force x time maybe as little as milli-seconds). Currently the hook or un-welded eye connections on the turnbuckles are weak. So on a continuous bumpy road that instantaneous maximum is exceeded again and again until the woop-ti-do where everything fails. Torklift solves this problem by adding a spring to dissipate some of the energy, but with a 6" space it makes it difficult. A spring by itself reduces the peaks but also friction is needed to dissipate the energy. So, by connecting the camper to the truck with strong webbing with over 5000 lbs of strength is sufficient to prevent the turnbuckle failure, but then what's next. I did some experiments using some 16" climbing slings. With two raps of the double sling, that's like 20000 lbs of holding power and connecting the loop with a stainless steel quick link they loosely connect the camper to the truck, maybe and inch or two of slack. What is needed is a way to tighten the connection. I'm thinking that the eye bolt connection to the truck bed should be free turning. Then a self, locking nut is used to tighten the eye bolt, imagine using a drill driver set to a fixed torque tightening the nut from the bottom of the bed. First off the sling twits until there is sufficient torque to tighten the nut and the drill to maximum torque. Now the sling has twisted 2 or three times and the system is supplying a fixed holding force. When more force is encountered, the slings tend to untwist evening out and dissipating the energy.
Just a though, I think it could solve the problem.