HA HA. I was thinking your van could be the toad behind my van, since you have a T-case (granted, the Ford auto tolerates towing well enough, within limits).
But yes, at one point the plan for the bus was to tow it with the van, and have a long double-stack trailer behind the bus. The van tows the bus better than the bus drove itself, when it ran. (Bus = 35 MPH tops on a 7% grade, compared to 70 up the same slope when its being towed by the van). Yes, it would require a multiples endorsement, and I would need to either change the van's registration or buy a trip permit every weekend.
In OR, a trailer bus is intended for carrying passengers, and unlike an RV-trailer, it does not have to be a 5th-wheel to ride in it. I actually started looking into it after seeing the Park Service does it: