Trailer Hitch For One Wheeled Trailer
 

Allows the trailer to bend left or right to track the car around corners, and tilt up and down, to follow grade differences between the trailer and car (Driveway ramps, for instance), while not allowing the trailer to fall over on it's side:

If the hitching U-joint is mounted High Enough the pendulum effect will make it always want be belly down due to center of gravity.
The only downside to this is as the car pitches side to side it will force the tire to scrub left and right the distance based on the separation of the U joint and the tire. This is really insignificant as far as fuel economy goes ,as usually a driver is going under 10 mph when these type of terrain situations are encountered.

The hitch will be mounted half way up. The trailer front will be a hemisphere sitting in a shroud which has a circular cut in it to snug the trailer front into. (See Illustration below)

Dips in roads at speed need to be accommodated. The hitch will act just like a ball hitch to allow pitch and yaw changes freely, but like a solid shaft to allow no roll.

That means you're going to have to reverse it like a trailer too.

Not so easy when you can't see it at all.

The pivoting caster wheel concept is the most popular single wheel solution for a reason.

This is what I mean by roll scrub
http://ecomodder.com/forum/attachmen...1&d=1518926854
Of corce the sight wants the picture sideways, ough.
I don't think it will add much if any strain on the system. Only side effect I can see is the single fixed Tire having a tendency to try and turn. similar to how you steer a motorcycle by leaning ( even drag bikes with 12" wide back tire that is square as a car tire still leans to induce the effect I'm speaking of, for turning).
Any ill effects would be most noticeable while high G-Force turning or severe side wind that causes body roll.
The greater the distance from the Roll center of the car and the U-joint Mount point the greater this effect will be. The Pivot Point must be at a central location as per the body shape and proportions through design you may be able to cheat this location towards the Roll center to minimize any ill effects. This is along the lines of what I was thinking as far as being able to do a one wheeled trailer behind a motorcycle/ bicycle.

I will be using a rear view camera in the collar. In it, the trailer will be visible.

Why would a two wheel trailer not have this problem?

OK, how do I find the roll center of a Gen 3 Prius? f I have to, I'll re-position the U-Joint.

What are you going to be using for a wheel?
I don't think I have ever seen highway service bearings and tire on a caster.
Then how easy will the tire be to change?
I have had a flat on my regular trailer. I had a hydraulic jack and my 1/2 drive ratchet, took less than 10 minutes to change.
I have worked on these larger casters before and I hate changing tires on them. When you pull the idler shafts out you have to open up the bearings, potentially exposing them to dirt if done on the side of the road.
Have you ever worked on one before?

Changing a flat would be more difficult. I suppose an axle pin that can be pulled out one side could make that simpler. the only reason for a single wheel and tire is to keep the rear of the trailer as slim as possible,(license plate slim, in my case) but if the wheel(s) were moved forward to a wider part of the trailer, a single frame rail with a drastically shortened axle mounting two wheels in the conventional hub mount manner could be used. Not sure how that would affect tail wag. I prefer to keep a single wheel as near the rear of the trailer. Another option would be dropouts (with a lock cap, as on the lower end of a piston rod) to allow the wheel to be removed like a bicycle front wheel.