except of course the two largest deserts on earth, the Arctic and Antarctic.

Quite right though, a nylon would act somewhat like a sieve, keeping out the larger particles, but doing nothing to impede the finer. It's these finer particles that would be doing most of the damage, since they can work themselves further into the hardware.

I'd be looking at a SSD, minimizing moving components means less places for the dust to get into. As far as heat goes, I'd think about getting a processor that is significantly more powerful than your needs, that way it would never need to work particularly hard, and subsequently reduce your chances of frying it.