The smoke units in all of the ones I've seen have gotten too hot on the sides for me to be comfortable using them for any length of time.
I did a mod on a couple of smoking caboose models that solved that problem and also gave you plenty of smoke. I used an MTH HO fan driven smoke unit in place of the stock smoker. With a small modular power supply, I was able to adjust the amount of smoke to the level desired, and the smoke unit runs cool enough to stick it right onto the side of the shell.