Indiana, there are no laws prohibiting riding in a bumper pull travel trailer, a fifth wheel, a truck camper, or the open bed of a pick-up truck. There's a difference though between what the law does NOT say and common sense.
Have I ever seen anyone ride in a travel trailer or a fifth wheel in Indiana? No. There must be a reason why Indiana laws have no restrictions, yet people don't do it.
I had my wife drive the TT to the dump station this last Summer and I rode in the trailer. I learned a lot during that 5 minute ride through the campground! Yikes! Never again!