You might want to make yer own thread so we can follow both iterations of single wheel trailers without thread jacking.
Might I suggest you take a peek over at singlewheel.com and see what technology already exists that you can borrow from.
Singlewheel trailers today
Keep yer goal in mind. Yer over building yer tail which won't be carrying anything because you want to reuse most of the parts from an existing trailer. You can take the same approach as the single wheel motorcycle trailers which already has an internal hub with high speed bearings and a rim/wheel combo that can take the load. The wheel is easy to remove and service. A simple swing arm suspension with an integral coilover spring/shock combo will be able to handle the road shocks without killing yer budget or yer unsprung weight.
