Late in the thread, but here's another idea. A one-wheel trailer that could hold any thermo-formed box (custom shaped to your optimum boattail profile). No need for articulation clearances and could completely 'seal' to towing vehicle. Easier to backup and no jack-knifing.
http://motorcycletrailer.com/sw/imag...rrier1-500.jpg
http://www.smarterbuys.com/video1/SWmob1w.mov