I tried them on a 42' fifth wheel and didn't feel jack squat from it. I tried it a variety of places and never found anywhere that felt like it assisted.
Personally, if you don't already have triangulation stabilizers, start there.
Otherwise, here are more ideas:
http://learntorv.com/shake-shake-sha...stabilization/
And specifically, I like the SteadyFast better than the alternatives:
http://learntorv.com/product-review-...t-stabilizers/