If I'd been Avon planning a double-cross, I would have chosen to take Vila too. Would you really want the inventor of the Tachyon Funnel mad at you when there might have been a prototype still at the base or enough parts available to knock another one up? Given the weapon's unlimited range, ensuring that you were able to steal or destroy any such items and that transport and communications at the base were knocked out permanently so that another one couldn't be built later would seem prudent, and Vila's presence might have been necessary to get past any security systems.
Perhaps Avon was having one of his "Aftermath" style don't-take-life-unless-it's-absolutely-necessary days anyway, in choosing to take a handgun onto the shuttle instead of a base-destroying bomb :)
Re cave stories, I am an experienced caver, and I can assure you that creepy-crawlies only live near the entry points of deep caves. Creepy-crawlies need to eat too, and there usually isn't much food further in (no sunlight=no plants=no things that eat plants=no higher level predators). If you want to introduce some added tension in a cave story, perhaps you could set the story in a multi-level cave system. It is possible to get trapped underground by water if it rains unexpectedly while you are underground, so you don't know it's happening. Getting out may require going to a low point or crossing an underground river in order to get to an exit. I know of a number of cavers who have been drowned trying to cross an underground river in flood. The characters could thus be forced to retreat to a higher part of the cave, and have to decide whether to wait, hoping that the water level will fall, or to chance being swept away, etc. Lots of opportunities for angst, heroics, and character death as well as heart to heart chats :)
Other than that, deep caves are usually at around the average annual temperature (say 9 degrees Celcius), and frequently, though not invariably, wet and muddy. The water always feels icy, and is certainly cold enough to make your legs go numb if you stay in it long enough without protective gear. Not my preferred venue for a romantic tryst...
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