Check out Roly Nelson's 3x3 build for a small version -
basically a telescoping single place sleeper - of what you
are thinking of. I can't locate the details at the moment.
One problem with a larger version would be a good bit of
weight cantilevered away from the 'tow vehicle'. You'd have to
bolster the rear springs or use air shocks and such.
It might be more practical to base it on a single wheel trailer
or one of the dual wheel single wheel styles. These have a rigid
connection to the tow vehicle so that the trailer does not pivot
or turn. The single wheel or the dual single wheels are sprung
on a castor mount and they do the turning/pivoting, not the trailer
body.
Here are a few links:
http://singlewheel.com/http://www.cruiserlift.com/swivelwheel.htmlhttp://www.smarttrailers.com/http://www.doublehitch.com/dhbuy.htmlI find this design idea intriguing and have considered it
on and off. I think you'd need more than a 3.5 to 4ft length
to have something usable. And a dual single wheel set up with the
usual travel path of the wheels matching the tow vehicles
track [in-line with the tow vehicles rear tires] would be best.
I'd go out to maybe 5-6 ft in length too, with a full expansion
out the back once parked, to give you elbow room.
Here is a simple Paint drawing I did for a post to another member's
thread, who had an old but usable single wheel trailer and was
wondering how to utilize it. I can't find that thread at the moment
but here is the drawing - a basic illustration of what I think would
be easily doable in this scenario:
Click on the pic to get a larger view:

Of course, this is more for a TD scale unit but the idea can work
for a taller an a bit larger body as well.
Happy planning!
Cheers,
Norm/mezmo
If you have a house - you have a hobby.