I just completed our smooth out the ride project. We installed a Trailair tri glide pinbox. That helped the chucking by about 75 percent. Bridge transitions and large humps were still to bouncy .
Next I installed Monroe gas magnums on the trailer. Things got even better as far as chucking and bridge transition bounce but still was not completely satisfied with bridge transitions and chopped up freeways.
We had Monroe Reflex gas shocks on our truck. I replaced the shocks with Bilstein 4600 monotube shocks front and rear . WOW were we impressed. No more bouncing on and off the bridges. With all of the modifications we now have a very comfortable ride. The best we have had out 6 trailers in 25 years. I think the Bilstein monotube shocks will control the bouncing issue that you have causing your pinbox to bounce off the hitch.
This was a long and expensive project for us but well worth every penny spent. My wife and I are very happy with the outcome. Good luck with your ride.