I've double towed since about 1998. My old setup was about 73'. I've since changed the boat and the truck, but I am sure that I am still over length in just about every state.
I have never been pulled over for a length issue Nor have I heard of it happening to anyone. Not saying it won't happen to you, but I am of the opinion that if you aren't doing something stupid - like driving way over the speed limit, or weaving in and out of traffic, etc, I don't think they are concerned with the length.
2012 RAM 3500 Laramie Longhorn DRW CC 4x4 Max Tow, Cummins HO, 60 gallon RDS aux fuel tank, Reese 18k Elite hitch
2003 Dodge Ram 3500 QC SB 4x4 Cummins HO NV5600 with Smarty JR, Jacobs EB (sold)
2002 Gulf Stream Sea Hawk 29FRB with Honda EV6010