Very nice walk-through, Mark. One thing I would add, in addition to the secret mentioned by John, is that it's particularly difficult to navigate the underwater passages. You really need to move up and down as you look around. It's fortunate that there's an O2 recharger available, as you're likely to need it.
For those of you playing along with the series, be forewarned that Last Minute Shopping is one of the most intricate levels in the scenario, and because it's an extermination level, you have to explore just about everywhere. That said, there are a lot of secrets to be found, many of which are exasperatingly visible (the "If only I could get there" syndrome) and others of which are so well hidden that you either need to be lucky or to look in forge. You might want to revisit my tips for finding secrets before playing this level. Pay particular attention to Rule #3.
Mark, I'm ready for your post any time, but is there anyone here who would like an extra day or two?