Well, since I first posted this topic a few weeks ago, I figured I would report back.
As you remember, I was originally asking about air bag pinbox, like the trail air/flex air.
As I was ordering the pin box, the salesman said that I was wasting my money. I asked him to explain. He asked what hitch I was using(Reese 18K Signature). He expected the response and suggested that I replace my hitch instead with a PullRite 20.5k. He stated that there is too much play in the Reese, allowing for greater movement and contributing to the "banging" I was feeling while going over bridges or rough roads. The way that he explained it to me made sense. And the hitch was less than 1/2 of the pinbox I was looking at.
I then asked about the moreryde pinbox. He said that the pinbox was a great adition, but not really necessary.
I decided to pull the trigger and order the PullRite hitch and the Moreryde pinbox. I installed both(in about 1.5 hours) and left the next morning for Virginia Beach, from home(Syracuse, NY). Well over 1,000 miles round trip.
Here is what I found.
The hitch is much quieter. I am not sure why my Reese squeaked so much, but this one is absolutely silent. But more importantly, it is significantly a much tighter fit. The Reese was noisy since I purchased it new. I used to have a Reese 16k slider that was noisy too. But never thought that a tighter fit would make a better ride, but when thinking about it, it does make sense.
Overall, I would say that 75-80% of the rough ride was eliminated. Only extreme rough bridge overpasses can be felt. I do not know if I could do anything to totally eliminate that. But of the past 5 5th wheels I have owned, I am most happy with this setup.
I tow at speeds between 68-72 mph. The truck seems to like that RPM range. And slower or faster and it seems to shift into 5th gear frequently. Must be the right powerband or something.