Now it gets into semantics, as one state I checked, defined a 5th wheel hitch in their legal definitions as a "pinned draw hitch", which allowed motorhomes with a pinned draw bar to qualify. Also, there are only 4 states that require the 1st tow to be a 5er and that legal definition came from one of those states. That is the problem with laws, they are usually so poorly written that one can do things legally, which the subject line would lead you to think otherwise........Also, some states specifically state that their laws regarding double towing are specific to commercial vehicles and then have NO laws for non commercial vehicles.
You can NOT just make a blanket statement that my state does NOT allow it or that a certain requirement must be met for it to happen.
A good example is one western state says that RV's are not allowed to double tow, but they also make an exception that is buried in the small print. You can double tow in that state, IF, you are going from a state that allows it, to another that allows it and you travel the most direct route. I read their law several times and NEVER saw the exception, until it was pointed out to me by a state Trooper.