Bike touring trailers are relatively rare and single wheel trailers rarer still, but if you want to throw in some singletrack riding while touring, then you might well consider a single wheeler, such as the T2.
The T2 singlewheel trailer is a well-made Taiwanese design that incorporates a fully waterproof 70-litre bag. It's aimed at touring cyclists who want to travel really light. It has a single aluminium tube as its 'spine', to which plastic clips attach. These then hold the wonderfully waterproof and very robust rolltop bag, which attach to the clips with compression straps.
Hitching is done with a bespoke axle that replaces quick-release spindles (fittings are also available for Alfine and Rohloff TS hubs). The double hook hitch mechanism is clever, well-made and secure. It fits 26in/700c and 29er dropouts, but we also fitted it to a 20in Dahon folder (the T2's light, minimalist design complements a lightweight folding bike).
We loaded our T2 with 7kg of camping gear to add to the 5.2kg weight of the tailer itself. The ride on a 26in wheeled, steel tourer was fine; the low, light weight of the trailer meant a lack of the rock and roll that can be an issue with single-wheelers.
On the 20in folder, where handling can feel comparatively light even without a trailer, the bike certainly had more of a mind of its own, but this still wasn't really a huge issue. Off-road, the small rear wheel just seemed to skip and hop over most things in its way (no doubt a light but firmly packed load helped).
At £324.75 it may not seem cheap, but it undercuts most competing trailers, especially those with similar capacities.
And its faults? If it dismantled to a smaller, neater size, it might mean you could fit your gear and the projecting trailer elements into the bag itself (the rear wheel and strut are removable), which would be a bonus, and you'd be able to leave it attached to the aluminium tube too.