I think rear panniers are also forgiving when comes to vibration and jarring.

We have carried our disc drive net-book in our rear panniers for a bunch of miles without any problems.

I agree, moisture is the biggest problem. I use a UV filter to protect the lens, and leave the lens cap at home. It allows me to get quick shots even in a moderate shower. When the filter gets scratched, it is replaced. I consider the filter an expendable item.