Hopefully big5er will step in and correct me if I'm wrong here, but as Steve said, there's no length limit on a road tractor. But, when you carry a lod on a bed, it's no longer a tractor, it's a truck, no matter what type hitch. Most states have a length limit of an rv at 45', and 65' for combination. This is NOT reciprocal, so local law applies when you leave your home state, same as any other length/width/weight laws.
You have a lot of homework to do. Good luck.