I've been toying with this oddball pusher trailer notion I've had for awhile. I do not like the idea of a pusher trailer, as generally implemented, but I've been thinking about a 2 wheel trailer with a narrow wheelbase. What I envision is this - a pair of 26" wheels on a common axle, separated by about 10" of open space. Mount a sprocket on that axle, and the engine to drive it all between the wheels, then build a rack that encloses both wheels from the axle height up on the outboard sides. Pannier bags/baskets, a quiet, well muffled 4 stroke engine, and you'd have a heck of a stealthed power plant.
Having posted this, now I HAVE to go sketch it up.