Truthfully, for a caboose, I'd be looking at a pretty small smoke unit. I've done several for folks using the MTH HO smoke unit and a small DC power supply. I used a variable supply and put around 6-7V on the heater, and a series resistor to drop the motor voltage down to around 2.5 volts. I just tuned the supply voltage for decent smoke, but not excessive smoke. After all, the caboose shouldn't look like it's on fire, it's just supposed to be a stove! You might have to tinker with the motor resistor to get the right look for the smoke velocity. I just fit the stack to the existing caboose stack, and rig a simple mount for the smoke unit.