All the smaller units road terrible (wobble or sway side to side), or worse, bend and break the axles if you hit a pothole.  Krone and others make units with the rear carrier but,,,, they get expensive in a hurry.  We have a 4 basket Krone with only the 2 small wheels for transport and tractor speed is sometimes too fast.  Behind a pickup, you're asking for trouble.  Normally we just throw it on a trailer with the front end loader, transport speed like that more than makes up for loading time.