I am not to sure about the original question. The single wheel BOB's have caused bad crashes due to weight and speed on hills. They need a drag brake on the rear wheel beyond a certain point, and that is not an option as far as I know, outside of custom. At some point you are probably going to end up on a back road with a soft shoulder, some of these paved roads have unconsolidated tar into the road. with a double wheel you will be forced way into the road. I would only consider a single wheel for touring, for regular camping and riding of the type you are describing.

I would not use a trailer at all. You could easily get an untralight outfit going for what making a trailer will cost. Actually you don't need an ultralight outfit, just a backpacking weight one.

I would look into the Nashbar trailer if you want a trailer.

http://www.nashbar.com/bikes/Product...2_171082_-1___

Not perfect, but few of them are, and you could apply your skill to getting it up to grade rather than making a kludgey 2 wheeler.

What a lot of folks do is run panniers and a single wheel rear trailer, that allows them to carry massive loads where that is required, but not to do it all on a trailer design that will limit them. I have been conventional places where even fairly standard bike options, let alone trailers, made it impossible to get through. Bridges, overpasses, and borders.