Hanging a bike off the back of a gas coach using a lift might cause problems. The lift and bike combined weight can be as much as 1200 pounds. There isn't much in the way of framing behind the rear axle along with the potential of the builder adding frame extensions that might not be up for the job of holding the weight of the bike and the lift. The long rear over hang of the coach is going to act as a lever with the additional weight which will might cause a large weight shift from the front which can effecting drivability. You might even be reaching the axle weight limits for the rear axle once the coach is loaded for the road.
It can be done with some frame boxing and such but you best option is probably a trailer unless you move into a rear engine diesel chassis.