Well, I don't see how you'll get accurate chuffing from the water tender. You'd clearly have to have something tied to the driver rotation to get accurate chuffing. The only way I see this working for the chuff signal to be generated in the locomotive and piped back to the aux tender for the RS rig. Even then, if the locomotive is running PS/3, the chuff won't be accurately synced with the smoke unit. I think George was alluding to some of the difficulties of the chuff in the tender.
Now, you could start talking about crazy stuff like synchronizing the chuff in the tender to when the smoke motor was energized, that would sync them up at least. However, when you turned smoke off, you'd lose the chuff. But, you could then turn up the PS/3 chuff and at least have some sound for smoke-free operation. Triggering from the smoke motor would be fairly simple, I'd be looking at a reed relay to generate the chuff with a little filter to avoid interfering with the motor operation. MTH reverses polarity on the motor briefly to stop the motor quickly, so you'd need to filter that out. I'm thinking a diode, series resistor, and a small cap, probably in the 1uf range in front of a 5V reed relay.
