In the NP itself, the only (legal) camping is in designated backcountry sites. Pretty sure most, if not all of them, have bear proof storage units now.
I wouldn't pack a gallon of water. A good chunk of the Great Smokies are technically classified as a temperate rainforest. Unless it's a really, REALLY dry spell, there's a water source in every little valley.
This is nice to know. We actually didn't want to pack any more water than just our two canteens, but figured we'd play it safe. Nice to know now we can just have our canteens and be able to get water fairly easy.