I have a sedan, and the bars are required. When my new coach was delivered, they towed it with a 1 ton dually-- no bars. The rear of the truck only came up about an inch.
I have heavy duty cargo coils in my sedan and when I loaded the coach on the drive, just to move the 25' coach a few feet, it really brought the rear end down. Then again it was pretty smilar to what the 19' Bambi did too.
I would say get the bars and use 'em. Like John said at the very least it will create some added rigidity to the connection.....