RV and trailer lenght.

I believe that's what you have to do - get a permit. I heard of one fellow (second hand) who actually made up a measuring tape (the ones on a reel) and added an 8' section in the middle. When pulled over, he made sure it was handy to measure and show the officer just how long his vehicle was. If it's true, I would not want to be him when someone really looks at the tape!