Not so long a go I saw a photographer with some weird little changing bag. It looked like something for handling radioactive waste. He changed his lenses by putting camera and new lens into the bag, zipped it all up, slipped his hands into glove-shaped pockets at the sides of the bag, changed the lens and then unzipped it and took the whole lot out again.
When I have a backpack (almost always...), I try to use it as a cover, exchanging my lenses with it. Not as techie as the closed bag you saw, but helpful anyway.
Given what you say here, I can't imagine taking my camera to a seriously dusty/sandy environment, like the sand dunes I photographed in Namibia last year! My P&S survived, though not closing well that lid in front of the lens for a couple of days. I had sand in and behind my ears for two days after that...
Regards,
Adelaide
