look at your drivers license, & state dot site, you may have a restriction on length as is.
I know a lot of guys who are driving 18 wheelers with out a CDL saying its for private use only gets them out of that requirement. That may get you down the road, but what happens if you wreck someone? Are you covered? Will your insurance cover you? God forbid some gets hurt or killed, will your liability be in force? or will they throw the book at you.
I had one of my pals get pulled over in Indiana last year with his toter home & stacker trailer , he had a regular GA DL. The trooper thoght he needed a CDL, he was held for hours & then they let him go, busting him on the fact that GA DL places a limit on trailer lenghth, the exact lenghth escapes me at the moment.
I have an insurance agency & have seen all sorts of stuff that you can get away with until the big one happens & then you get stuck with the bill.