Good info, John- - - - -but there's one variation that didn't get mentioned- - - - -a bumper pull rig with a wheeled dolly supporting the tongue of the trailer. This setup would be similar to putting a hitch ball on that much-maligned tow dolly. The "advantage" is that tongue weight carried by the tow vehicle can be controlled better, since the position of the ball on the tow dolly can be adjusted to vary the amount of weight the tow vehicle carries. Most of the tongue weight of the trailer rests on the wheeled front support axle. Disadvantage- - - -like the vehicle tow dolly or a set of double trailers on a big rig- - - -don't even think about backing up! Those wheeled front supports actually date back to the earliest days of towing. There was an example of that system used with an early camper trailer in the Harrah's Club automotive museum in Sparks Nevada that I saw back in the late 1970s. I believe the tow vehicle was a Model A Ford!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!