I posted my experience with shimming the camper in this thread:
http://www.wanderthewest.com/forum/topic/9608-wheel-well-shims/?hl=shims
Since then, I have even better results after sliding the camper forward to touch the front of the truck bed. My theory is it is geometrically impossible to load a camper using jack legs and make good contact with the front of the truck bed. The truck bed moves in a motion controlled by the springs while the camper motion is different as it is controlled by the jacks. Neither the dealer or FWC factory installers were able to make good contact with the front of the truck bed using the jack legs (they jostle the camper forward the last bit if so inclined).
I shimmed my empty camper at the wheel wells to prevent side-to-side motion, loosened my turnbuckles, and stepped on the brakes firmly (not violently) while going downhill at slow speed (5 mph) and then tightened the turnbuckles before going back up
. Measurements before and after showed the camper moving forward 1/8". My turnbuckles have never loosened since nor has the camper moved with the camper firmly against the front of the truck bed and the wheel wells shimmed even though I have a very slick and smooth truck bed (no liner). My opinion is needing to tighten turnbuckles is a sign of camper movement not turnbuckle loosening. Initial turnbuckle tightening is required as the camper flexes and settles into a loaded alignment. Assuming a correct amount of torque is applied to the turnbuckles (not too much or too little), future turnbuckle tightening would be a sign of camper movement.
Super tight control of the camper motion is important for our long trips but for short periods it may not achieve much. Camper movement increases as the camper polishes the truck bed. More frequent loading and unloading and short trips will prevent or reduce bed polishing.