I used a single mesh. The attach component didnt seem to work very well.
Made back wheels copy rotation data from the driving back wheels so they turn.
Added a constraint for the trailer part of the mesh and restricted it to a sideways angle.
But you need to remove the physics volumes of tires that are being “faked” But then i found the trailer goes into the ground so i had to add an additional box collision at the bottom to fake wheels being there.
Then its a careful process of tweaking the friction of the bottom box collision. Too much and the trailer holds the truck back. Too little and it just glides around like its not a trailer… more like a hand from the movie idle hands.