Most of the time, you need to carry along a few things to help stabilize your fifth wheel. Even if you have a sophisticated leveling system such as the Lippert Ground Control 3.0 on my RV, and even if you park on concrete, you will still want to "stabilize" your RV. Otherwise, it will tend to rock-and-roll as you move around inside... you might even get seasick.
While this page specifically applies to fifth wheels, much of the information is valid for travel trailers as well as motorhomes. For fifth wheels, there are two primary causes of movement; the suspension as well as the sloppy fit of the landing gear. The suspension of course includes the trailer tires and springs, as they are dynamic in nature and designed to move. Unfortunately, they move equally as well when the trailer is at rest as it does going down the road.
The landing gear typically consists of three square tubes located at the front of the coach, and move up and down to not only level the trailer, but also to facilitate the hitching process. These tubes of course necessarily have some slop in them so that they can move.
Most trailers also have rear stabilizers... either cylinders such as I have with my leveling system, or jack-type mechanisms that can be either electrically or mechanically operated.
The best stabilization techniques will consist of several methods, each tailored for the particular area to be stabilized.
Landing gear. There are three different options here. The least expensive option is to simply build up a couple of wood blocks so that the landing gear is not extended a lot. Less extension means less slop.
The second method for stabilizing the nose of the fifth wheel is using a tripod for the king pin. A tripod will effectively stabilize the front end of the trailer and is the method I use most often. The only downside to using a tripod is they can be heavy, and a place to store them must be found (I put mine in the bed of the pickup.
I bought the BAL 25035 Deluxe Tripod, which is probably the most heavy duty tripod you can buy. Unfortuntely, it is awfully heavy, and due to the lighter weight of my RV, I could have probably bought a less expensive and lighter weight unit.
The primary difference between the tripods is how they adjust in length as well as what kind of "spreader" they use at the base. Caution; they can be a trip hazard, and many people tend to put two legs of the tripod forward, and one leg to the rear.
The third method is to use stabilizing bars, such as JT's Strong Arms. They are effective, but add weight to the trailer. And many fifth wheels - especialyl in the lightweight category, do not have an adequate frame member where the attachment points are. So you may end up modifying the frame to use them. As well, they work best when some load is put on them - i.e., after securing, you raise the level just a bit to work the slop out of them. This is not as easily done with a leveling system, as you often have to manually level it for the best results.
For the rear, many people use X-Chocks. X-Chocks are brackets of sorts that fit in-between the tandem tires on each side. When in place, they are cinched down until they put pressure on the tires so that they cannot move forward or rearward.
However, with the Ground Control leveling system on my RV, I did not find X-Chocks to make any difference. I am sure they work better with RVs without a leveling system as many people attest to their effectiveness. But they did not work for me.
Regardless, for safety, you should use some kind of wheel chocks to prevent your RV from moving, especially if not on level ground, and during the hitching process.
I did find though that a set of manual jacks on the rear of my coach helped a little bit. Again, this is mostly likely to the Ground Control leveling system I have on my rig as manually stabilized RVs typically already have some sort of rear scissor jacks.
So again, the best solution for you will be dependant on what kind of leveling or stabilizing system you have on your rig, and will be a combination of solutions. Again, for me, I combine large height blocks under the landing gear, a king pin tripod, and manual jacks on the rear frame.
(anyone want to buy a set of X-Chocks... only used once?)