Ken,
There are a few different websites that give information on double/triple towing in various states. At the moment, I can find but one of those, which I will link to below.
I think this one speaks of "triple" towing meaning three units (tow vehicle/fifth wheel/towed vehicle) and there are a number of states in the East that do not even allow that configuration. One of which is Florida. In other states, you might get into trouble with the length of the combination of vehicles.
Also, some areas have numbers in the columns after their notation, and those numbers relate to footnotes. Those footnotes can be accessed at the bottom of the page.
http://www.towingworld.com/articles/TowingLaws.htm
Hope this helps you some.
Terry
Edit: I found another link to double towing. I have not compared the two for any discrepancies, so I suggest checking both.
The second link is here:
http://www.rvsafely.com/rvroadlaws.htm