You can get "stabilizing jack stands" at Walmart in the RV section (four for $50).
When I put our new 2017 Forest River on a permanent site, I used them. I put them under the frame at all four corners. That helped a bit, but not enough. Then I used four more and put one under each wheel axle shackle, and that made it even more solid.
I finally added concrete block piers with shims. Three on each side under the frame and that made the unit rock solid.
Naturally if you are moving the trailer around you can't do that, so you'll have to put up with some movement.
Jack L
