I used one heavily for years, and still have it. Lasted fine. Needed to clean it a little from time to time, but no big deal.
The weight, or thickness of the canvas is important. Of course the military surplus stuff is pretty much indestructible.
The one I referred to earlier is an October Country bag. It is as thin as you want to go with canvas. Any thinner, and there will be problems with it holding it's shape.
Remarkably durable material.