Don't forget you also need a weather sealed lens to get full benefit of any weatherproofing.Yes, good points! I'll also add that some weather-sealed lenses need filters to complete the weather sealing. Sand and dust are the worst!
The other thing you need to watch out for is if you'll be in an extremely dusty environment such as the desert. The dust can be very fine, and tends to get into everything no matter how sealed unless you provide additional protection.
I also like to protect from sea/salt spray if the ocean is rough.
Edited: I'll also add that I always make sure that I have the rain covers for my thinktank belt pouches (which are attached) and the rain covers for my camera bag/backpack to protect the rest of my equipment (don't ever take those out of your bag).
I'll add that the weather sealing isn't perfect, and with long term exposure to the dust & sand you can still get damage. For example, I was at Burning Man this year with my 5d3 and my 24-105 on basically the whole time. UV filter on the front, a bit of gaffers tape around the lens/body part. I thought I would be fine. Not so! Repair bill with 30% CPS discount came to a bit over $900.
So, if you're just going out hiking for an afternoon and don't plan on being in a whiteout dust storm, even if it's dusty, you'll almost certainly be fine. If you're going to be out on an alkaline dusty desert for a week, do something to seal up the vulnerable parts of your camera AND lens. Sea spray is probably just as bad, especially if it gets inside.