I live in the driest state of Australia (South Australia) - and have been to some environments which are dry, dusty and sandy. When the wind is blowing in these locations, I don't change lenses... though occasionally I'll change lens (not near the ground) at the beach, if I feel it's safe.
After tens of thousands of photos, I've had one or two specs of dust on my 7D's sensor as a result, but thankfully with my rocket blower have removed them. The 15-85mm - though not rated 'weather sealed' is definitely a step up from my former 28-135mm - which got dust (and 1 or 2 pieces of sand) in the zoom, but thankfully I could remove them (coax them out using gravity and a fine bit of paper, as they were still near the join of the zoom)
I also have the 70-300mm L - which is a step up from any non L lens...it's built like a tank, and tolerances are tight. I carefully brush off sand / grit / dust from my 7D body and front of lens. In spray conditions I do use UV (or CPL) filters - which I can wash off later (easier).
Best wishes for your trip. In extreme conditions, I'd probably not go outside with the camera, unless you have some protection (eg designed bag, etc). Then again, you probably don't want to go out without eye protection in a true sand storm either!
The photo & story of interpilot, and the post of tgara also share some telling situations. Do be careful, but where the weather isn't extreme... you should be ok (as long as you don't change lenses or filters), so enjoy it then!