Here another site.
Towing World
Look at the info for triple towing. Like the site above, Florida says no.
The term triple towing vs double towing is debated frequently on the forums. And while towing two trailers would seem more accurately called double towing, in the RV world it is called triple towing, a tow vehicle and two trailers.
Here is just one of many
articles about it.
Just a few days ago I saw a Montana passing thru town with a 20+' pontoon "party" barge behind it. Don't know how long it was, but had to be beyond most legal limits.
Some have stated they pulled thru states that don't allow it, but never got stopped. But some others said they did get stopped and were not allowed to proceed without dropping the second trailer on the side of the road.