Glen, I haven't used the WS product myself, but there's a reader's review available here. It doesn't specifically mention tunnels, but the reviewer does say he has some hard to reach areas. Possibly you could post a comment asking him for more info?
For some hard-to-reach areas, it can be handy to use a track eraser attached to the end of a yard stick or similar. It can reach locations where your hand is too big, like through a tunnel portal. You can cut down the stick or eraser to fit.
Rob Spangler