I have used a neoprene action cover for my DSLR ever since reading about them in an excellent 'primer' on building a DSLR system.
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As I often use a variety of rucksacs etc, rather than a bespoke camera bag, when out in the hills, I needed something similar to protect my additional lenses. This neoprene 'tube' with a drawstring closure and clip-on hook system (belt attachment) is available in several sizes. In my case I purchased three of them (different sizes) for Ultra Wide Angle, Telephoto and a specialized small prime lens that I usually carry.
They seem to work fine based on 2 months experience. You really can pack and forget...
Different brands are supplied by Amazon from time to time but I believe they all serve the same purpose pretty well. Generally well worth the outlay.