The in game brandt does it fine and other modders can do it such as the FDR Logging lowboy. While Giants could make it better, it's not totally on them.
Then there are some of the heavy equipment you haul.
I can haul the FDR excavaotors, the john deere 848 forwarder and 843 harvestor and they tie down and stay put. But the FDR Clark cable skidder slides around no matter what (in fact, it sometimes slides on it's own while parked on flat ground).
I think the issue is sometimes with the mods you're hauling and not with the trailer itself.