Here is what I pull, total length: 71' 2"... Haven't been stopped yet :d **knock-on-wood** lol
81 feet is pushing it. Not sure what situation you would have to be in for them to check the length, but 6 feet over the limit and 16 feet over the limit are pretty big differences... expect someone to notice.
atleast thats wat it is for semi's. i drive truck and im assuming rv's would have the same rules. and a 5th wheel and boat is not a B-train. its called A-train. B-train is both trailers attached by 5th wheels. lol