I have what I believe to be an important consideration.
I have broken 3 center bolts on my tandem 7k axles' leaf springs. At the national rally, I discussed this with the representative with Dexter Axle. He was pretty emphatic that the only way there should be significant shear stresses on the center bolt is if the u-bolts are not sufficiently tightened. He showed me the specs for my 1/2 inch u-bolt, with flare nuts as being 70 ft-lbs. Since the rally, I've checked the u-bolts that I know were tightened to spec during my disc brake upgrade at the rally. With the weight of the camper sitting on the leaf springs, I was able to tighten each nut several turns to hit 70 ft-lbs. I believe the weight of the camper eliminates any gap between the leafs of the leaf spring, reducing the bolt/nut torque. Time will tell, but I'm hoping that since I've tightened each of the u-bolts with the full weight of the camper on the springs, I will not have any more issues with center bolts. Time will tell...