Judy - I travel a lot around Aus - preferring remote places - I take my 40D, 5DII and L lens with me everywhere. They are always in the 4WD within easy reach - yes they get dusty and have a few bump marks on them. One of my lens rolled out of the car once and onto the ground when I jumped out to take a photo. Sometimes they get bounced around in the vehicle and I usually put a pillow or similar around them. I guess I should treat my equipment with more care, but it's too time consuming extracting a camera from a dust proof bag everytime you see a photo opportunity, the moment is often lost. Been to Cape York a couple of times and even to the north of India which was very dusty.
I haven't had a major problem with dust inside my camera and lenses.
Lesley