Put a good heavy hitch on it.
I couldn't resist...I was kidding...seriously, dig through the forums and you'll find a lot of toy haulers with pictures of how they converted it. There are buses that have had the bodies shortened the the rear half of the frame used as a 5th wheel (I considered doing that with a long bus and using the frame as a flatbed hauler) and others that had ramp doors made in the back to pull the toy inside. I just haul a trailer with mine. The first question is what kind of bus do you have or are you looking at?