I have a 20ft ski boat that we triple tow (Waverunner in signature is old picture) it is only 2300#'s. All combined it makes our pull unit 64.6ft.
Tow laws vary from State to State and if they allow triple tow, you still may be limited to overall length of your pull unit (Truck - Trailer - Boat).
Try looking at the link below;
http://www.towingworld.com/articles/TowingLaws.htm