m-angler:

I've tripped with down for at least two decades. I like granite gear compression sacks lined with good garbage bags (steel saks the preference), the garbage bags get folded closed (twist em and you can't effectively compress the bag) and then the bag will compress to the size of a cantaloupe (15 degree bag). The combination of compression and trash bag is very water resistant. I've yet to get my bag wet and I don't use a pack liner.