Several years ago, I saw a comprehensive state-by-state list of towing laws, including the legality of triples. I could have sworn it was on the Blue Ox web site, but I couldn't find it, so I sent them an email. Their Customer Service Rep Tamra Krugman got back to me quite quickly with a pointer to
http://www.towingworld.com/articles/TowingLaws.htm. For some reason this site doesn't come up for me in Firefox, but it seems to work fine in IE. Towing World is apparently part of the Blue Ox company somehow.
The list has a lot of info, but to summarize the situation for triple towing. Triple towing is flat-out illegal in 21 states. Several other states limit it to 5th wheels. It is total-length-limited in most others. Triple towing is legal in Louisiana, with a limitation of 70 feet total length.
Thanks, Tamra.
Bill