One thing I found to be true for the Crossover scenario - if no-one has flight, and it is a later turn when the bomb is revealed, there is no way for anyone to get there with regular movement, so what I did, is added a "zipline" that called the cargo transport line, that someone could use as a move action. If they pass the random peril, they can drop off the line anywhere along its length. If they fail, well, they fell off Xd6 down the line. Of course, I always opened the bay doors just before they rolled...just to give them something to think about if they were going over them.