I use a bag that I found in Belize about 15 years ago. it is actually a camera bag complete with good foam padding all around tatally encased in the canvas covering. So it is water resistant on the outside and the inside and can take a drop without too much worry.

I guess that the only drawback/advantage is that it is a soft bag so if a car ran over it, i doubt it would be protected. But it is very practical.