Our 5th wheel has two 12 inch I-beams as the main part of the frame. With such large I-beams I was surprised at how much give there is. I decided the I-beams must be made from a bunch of remelted foreign import cars.
The JT Strong arms seem to help based on what I've read. I don't have them but I do use a homemade Tripod on the kingpin. I fabricated it out of square tubing and some other parts I had laying around. It makes the front half of the 5th wheel solid as a rock. The stabilizer jacks at the rear help make the rear less bouncy....But we still get some bounce in the mid-section from the suspension. We have learned to live with it.