Camping World used to sell the HWH leveling system for trailers - as I recall a 4 jack system was around $3000. Since most 5W now have powerful electric front jacks (the "landing gear"), I would think a pair of rear jacks, perhaps electric rather than hydraulic like the HWH system, could be added for quite a bit less.
If you only need to stabilize rather than level, i.e. get rid of the vibes, that's fairly straight-forward. First you need sturdy rear stabilizer jacks, either manual or electric, if you don't already have them. I further recommend locking chocks for the wheels, something like a Chock & Lock [ http://www.campingworld.com/browse/skus/index.cfm?deptID=&subOf=71,33&skunum=19342 ] or similar product. These stop the wheels from rocking as the springs flex when people walk around in the rig. Last, a king pin stabizer helps a lot - see http://www.campingworld.com/browse/skus/index.cfm?deptID=&subOf=33&skunum=20307&src=TSC
You may or may not need all of these, so I would go one step at a time until the problem was solved.
If you already have rear stabizers, they may not be strong enough to apply a sufficient stiffening pressure to handle the vibrations you are experiencing. Or maybe you aren't cranking them down tight enough. Some people use a 1/2 inch drill/driver to power-crank them down. An 18V cordless does the job nicely. Some units aren't very strong and will been or flex under pressure - if so, they will need to be replaced with better quality. And many rear stabilizers have tiny foot pads that quickly work into the ground and relax the pressure. Placing a sturdy board under the pads will help a lot. Try a piece of 2x6 or 2x8
