trailer saver makes two different hitches, one designed to drop into standard rails on a pickup box, and one with a flat plated designed for a mdt/hdt. I used the mdt/hdt version, and yes it has to sort of recess down between the frame rails to get the pin height correct as does the ET hitch. I don't know of any air hitch that is a "bolt on" for an hdt frame, they will all require mounts to be fabbed.
Exactly where you place the hitch depends on the frame height of the truck vs. the pin height on the trailer you want to tow. I did see one picture of a trailer saver on a hdt where they had it on a flat plate directly on top of the frame rail, but other than that all the ones I have seen have been recessed.
The one is mine before and after I built the bed:
|