I think with a bit more research you will find laws for double towing is a State by State deal. With respect to these issues, you have to abide by each states laws no matter what your state regs are same goes for length. If you chose to tow over length or doubles in states that don't allow it you may get by no issue, but maybe not.
This has been discussed at length on the escapees forum on the HDT section. If you go there you will find a lot of answers. Try a search or post there.
http://www.rvnetwork.com/index.php?showforum=32
Here is a thread that discusses this very thing
http://www.rvnetwork.com/index.php?s...6&st=0&start=0
Also mentioned is the options to towing double.