Maybe I've been lucky... On a 2 year bicycle trip it was just an M4 and a couple lens, no problems. And although making photographs is one of my main enjoyments 'seeing' when I travel I still carry just one camera. Having a very high quality compact outfit is my main consideration and not being loaded down with gear that can make the type of travel I do a backache. I'm basically a one camera, one lens (at a time) kind of photographer anyway. For the last 10 years or so even though I have a great Leica outfit I've taken a single Rolleiflex (love the square and big picture), also without problems in dust and cold/heat.
Now that said all it would take is a one time camera failure to change this. And if I was going some place where I really thought I was going to be changing lenses a lot I would probably take a couple cameras (one Leica and the Rollei or two Leicas) with the idea I had a 'back-up', but till then I guess I'll stick with the easy to carry way to go - knock on wood.