I like to use a trash compactor bag of a suitable size inside my pack. I don't use a pack cover if what's in the outside pockets can get wet and no problem, which is what I prefer. If I've got stuff in outside pockets I want to protect, I use a Zpacks cuben pack cover, but I'd still have the compactor bag inside the pack.
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"Keep it light" . . . . QiWiz
Obsession just means you care