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.