Vwbeamer; I think the one-wheel trailer as a "rolling boat tail" has some merit.
Pros: you could make the boat tail longer, therefore possibly more effective.
Being a trailer, it could provide functional storage space that would be easier to access than a bumper-mounted tail.
It could be hooked on for longer road trips, and easily detached for around-town driving.
Cons: Cost and hassle of getting it registered/licensed as a trailer.
Extra rolling resistance of the tire.
Another possibility that I have not seen accomplished to its full potential is a tail supported off a hitch receiver. This would enable a longer tail, be lighter weight, and eliminate licensing costs, but would lose the convenience (attaching and detaching) and functionality (easily accessed storage) of a separate trailer.
I think the one-wheel trailer would be an excellent way to go if you need a light trailer for road trips (family vacations? Yah!). I would love to build one for my family car. Throw the luggage in the boat-tail/trailer, and leave the interior open for the kiddos.
