Our x18D has some shake to it with the 11 year old flipping around in his bunk.
The BAL wheel chocks that go in between the tires makes a huge difference - one of the better investments we made.
I also find that i have to go around and sure the jacks up every couple of days when camping, they seem to loosen up.
there is a delicate balance between the tongue jack and the stablizers. Meaning, that after i go around and drop the stablizers i need to give a crank or two on the tongue... All these things helps make a solid trailer.
Then again, this all could be nonsense depending on the ground you are canping on