Which containers inside of Fort Dawnguard are considered "safe" storage? Which ones re-spawn? I would think that the fish barrels would re-spawn, but are the many chests throughout the fort safe? What about other barrels that are not labeled "fish" barrels, and sacks?

I would assume there all safe, but i use the chests in the hall opposite the 'cave' like contruct, with the dog kennels... they've stayed safe through my whole DG playthrough..

I thought they were safe, but the fish barrel near the grindstone reset and I lost all my blacksmith elixirs

I learned the hard way about fish barrels in Riften. I lost a bunch of smithing ingredients there.

Lol don't you get a room? Same floor Isran has his room.

Yes, I do get a room, but I like to store things close to the place where I will be using the items, hence the original question.