Generally a hitch upgrade such as the Trail Air replaces a
portion of the trailer's existing hitch. Typically an extended pin box mounts to a fixed set of brackets on the trailer's nose. The extended box gets replaced with the Trail Air or similar brand. There are several common designs for pin boxes, as shown on the Trail Air site.
I helped one guy install his Trail Air and talked to another owner. Both are very happy with the results, claiming it reduces the fore-and-aft pitching motion you encounter on some road surfaces (e.g. "rumble" strips), RR crossings, etc. Of course, everybody tends to praise things they just spent $$$ on.
