I haven't done it personally, but I spent about 20 minutes talking to a guy next to me at a truck stop who was pulling his YJ behind a 5-er toy hauler.
He commented that, legal or not, there were a lot of highway patrolmen out there who didn't know the law when it came to towing doubles, and he'd been stopped multiple times. He ended up carrying a copy of the California Vehicle Code section that refers to doubles. Luckily, he'd never been cited, as the officer's couldn't come up with a code violation to use on the citation.
The other consideration is the length of your 5-er. I have a 38' Next Level, and combined with the length of my crew-cab long bed dually, I can't add the TJ behind it without going over the max length limit.
2006 Black Unlimited 6-speed, Rubicon Express 5.5" Long Arm Kit