The tracking of the trailer has very little (if anything) to do with the stance of the wheels. It is the longer tounge that will keep it tracking behind the two vehicle. It will still blow around when a semi passes you, or you the semi, but it will not jerk the tow vehicle around as much and will recenter in a much more gentle way than a short tounged trailer will.
All other things being equal, for an equivalent disturbance, the wider trailer will have larger oscillations in the disturbing, restoring and damping forces due to the longer moment arm from the tow point to the tire contact point. In particular, the component of the tire side force that resolves to a force pointing directly aft and acting on the moment arm, sin(yaw)*(axle length), will have a much larger impact on the system on a wider trailer than on a narrower trailer.
Assume a wind vane with a pivot arm of length 1 ft from the pivot point to the center of lift of the vane. Assume a second wind vane with the mid point of an arbitrarily long cross bar attached to the same 1 ft arm with a vane at each end of the cross bar. Any length cross bar will be less stable than the zero crossbar case and with a long enough cross bar, the wind vane will be unstable.
Looking at it qualitatively, an absurdly long crossbar (axle) will, in effect, result in a very short pivot arm (tongue length).
Please don't make me draw a free body diagram.
