I've gotta build one of those! I always liked the train (headlight) coming down the dark tunnel in some haunts and the steam locomotive coming toward the tour tram at Universal Studios, but I could never figure out a way to incorporate one of them into a haunted house and make it not seem out of place.
But the truck is perfect! Until it moves and you hear the horn blast (I gotta have the horn too) it looks like it belongs there.
Now, how to make it work. I suppose I could use some really long air cylinders, but some kind of spring setup seems like it might work as well. But I would need someone constantly resetting it, though. The best thing about using air would be that you wouldn't need to mask the sound - it already sounds like the brakes.
I'm going to have to work on this and I also welcome other's thoughts, as I'm sure Smiley does. And I thought I had storage problems before.