As I've pointed out to you before, we have the sister Flagstaff 8529IKBS.
There are several trains of thought to help with this and most have been mentioned.
A. X-Chocks between the wheels & tires.
Get the narrow, not the extended version and you'll still need to crank them tight together to get them between the tires. Then, once inserted, tighten between the tires to stop the 'rolling' movement
B. When leveling, leave the front just ever so slightly low and then run down your rear stabs. Once they are down, raise the front end back to level with the front jacks.
This will allow you to put just slightly more pressure on the rear stab than what you are able to do normally.
C. Obtain two scissor type jacks and use under the axles on each side to reduce the bounce in the center. Because of the design of the torsion axle suspension and the lengthy distance from the front to rear stabs, you really need something there for support. Harbor Freight has them very reasonable.
JT's Strong Arms or SteadyFast systems.
Either of the methods above will remove about 90 some percent of your jiggle.
Then there is # 3.
Combination of both.
It just depends how susceptible you are to movement and how much you want to do during set-up.
2016 Flagstaff 8529IKBS Diamond Package 5th Wheel
Ford F-Series SCREW 4x4
TST Tire Monitor - Sinemate 3500w Gen.
2016 Nights Camped = 42