The Hyrail concept is an interesting one that hadn't occurred to me. That has merit. The problem with a fire truck is that it would be higway bound and much of our area would be inaccessible.
But a Hyrail vehicle with perhaps a 500 gal. tank on the bed with a pump and equipped with attack lines might be a good answer. I have seen many Forest Service vehicles equipped exactly that way. It would be perfect for dousing spot fires. Perhaps the Forest Service has an older, but usable, unit they would be willing to part with. It could be equipped with a Hyrail mechanism, and we are in business. Anybody out there on speaking terms with Smokey Bear?
As far as the rotary tank car with sprinklers are concerned, I doubt seriously that the little additional water from the sprinklers would materially increase plant growth. Consider that the water would last only for the minute it takes the train to pass.
As far as backing the train down the grade, that would be a concern. Maybe Coker could speak to this.