I use both. The stuff inside the liner bag is stuff that has to remain dry (extra clothes, sleeping bag, stove and matches/lighter, etc). Anything outside the l

I use both. The stuff inside the liner bag is stuff that has to remain dry (extra clothes, sleeping bag, stove and matches/lighter, etc). Anything outside the liner but still under the cover is stuff I'd prefer remains dry-ish, but can get wet. I made my cover out of Silnylon; it weighs very little compared to the added peace of mind