Please turn your caps lock off.
I agree with Mark B, you want something to stop your tires from rocking back and forth. Go outside and watch the wheels as someone walks around inside, you'll see the wheels rolling slightly, that is where you are getting most of that movement feeling.
I'm guessing this is at a permanent or semi permanent site? If so, perhaps you consider putting it up on some cinderblock piers at the corners, then every 10 feet or so. Once you have it nice and sturdy, let the air out of the tires to settle all the weight on the piers so your tires and suspension aren't holding it up at all.