Since you are asking Arizona, it is 65' Bumper to Bumper (there is no RV exemption). Your Boat is Cargo, so doesn't count. I am exactly 65' Bumper to Bumper, but 67' with the boat and so am legal, you may be too.
Here is the disclaimer, Cops are generally as dumb to the law as you and I, example, in Phoenix drivers of Motorcycles are frequently ticketed for driving in the HOV lanes with only one up, even though there are signs every 500' saying Motorcycles are legal, and the sign has a picture of a motorcycle with ONE rider.
You can still get a ticket, you will have to defend yourself if you do, but the odds of getting a ticket are very, very slim. However, have an accident over length and your insurance agent becomes your enemy, just like overweight, you are held liable, legally too, and can be ticketed after the fact.
Arizona specifically states that an RV (truck or other) may pull a second trailer or combination of trailers if the middle vehicle or trailer is equipped with a fifth wheel.
Well this is stupid too, the TRUCK has the Fifth wheel, not the middle vehicle, it has a pin.....
And elswhere it states that the maximum vehicle length is 64', no exemptions without permit.
DM