I have nothing more to add on the rivet replacement approach unless you have an additional question. However, something to consider is that on multi-lane highways the outside lane of traffic is always rougher than the inside lane(s) due to traffic volume and the fact that the where the pavement transitions to the shoulder erodes away first because it is not supported/surrounded by paved road itself, but is flanked by the gravel portion of the road bed as it transitions to the shoulder and then to the underlying soil where there is much more ground heaving, etc.
So the bottom line is if your tow vehicle and trailer are really getting beaten up, consider try driving on the inside lane(s) if traffic conditions and laws permit. Technically, here in Kansas, I could never legally do this because there is a state law that is posted on the roadside that states something to the effect DRIVE IN THE RIGHT LANE EXCEPT TO PASS OTHER VEHICLES. Now, if I needed to do otherwise for a few miles, I would drive in the inside lane as much as possible until I was out of the rough area. Also, sometimes changing your speed up or down will improve the ride.