How does using a tractor trailer to pull a fifth wheel camper down the highway legal for a non CDL driver?

The FMCSR grants exemptions for certain classes of vehicles, to include:

• Recreational vehicles
• Firefighting equipment and first response apparatus
• Registered farm vehicles
• Military vehicles

Pending certain criteria. In these instances, licencing requirements are left to the states in which the owner is licenced. In some states, they have non-commercial Class A and B licences. States in which retirees wield a lot of political power - such as Florida - allow these vehicles to be operated on a regular drivers licence. Vehicles of this type are dangerously unregulated, and it shows when they get on the road, but no politician will dare touch it, since retirees and the AARP wield a lot of power in the political lobbies.