I have a treadmill but prefer the road. Now that I'm doing hills I have no alternative (at least none near my home) to the mill. I'm doing the 2 hill workouts and a medium long run on the mill.
The indoor air helps with the eia but the intensity of hill repeats still causes a problem (I pre-medicate with albuteral which helps alot).
On the road I carry the inhaler but have only used it a few times this winter (on easy or long runs I almost never have symptoms).