The thing that wobbled our 5th wheel the most was going up and down the entrance steps. Simple physics would demonstrate that the weight of your average adult applied to a lever, (in this case your steps) would multiply that weight, turn it into a twisting motion and apply it to your RV.
Visions of The Poseidon Adventure come to mind.
The Stabil-Step Jack (Stromberg-Carlson Products, #JSS-7) fits under your steps and transfers any weight applied to the steps straight to the ground.
Put the life jackets away. That violent rocking motion is gone.
Heavy and overbuilt, one of these will outlast several RVs. Does exactly what it's supposed to do.
Getting it adjusted requires turning the threaded rod, put the step down and test for fit. Repeat. Repeat. Repeat. I like keeping a square of plywood under mine, though that is not necessary.
Camping World, on sale $22.22