Having towed non rv trailers for a living I've found its best to contact a state troop command post and ask those that do the enforcing how they enforce your questions. Do not assume the way you interpret a code is the way it will be enforced in that state. Do it wrong can be a expensive gamble. Do not assume just because your towing a rv trailer you will never be stopped for a violation.
And of course when talking with a dot officer/DMV person/etc use the correct terminology. Your asking a double tow...not a triple tow. Refer to a triple tow then of course the answer will be "no triple towing allowed".
Good luck
