Hi, I was given the quest to destroy the Dawnguard and after killing them I saw that I could sleep in any bed and that I could take anything from containers without it being marked as stolen so property is not a problem.

I went back with another character (way more than 30 days since the last visit) to check if the bodies disappeared and they were there.

I know that Fort Dawnguard has storage problems even if you side with them, but, once there is no one there alive, does it become safe for storage?

The same question applies to Volkihar Castle if you side with the Dawnguard.

tl;dr: After you kill the opposite faction does their fort/castle become safe for storage? .

Regards.

That's an interesting thought. I'm not sure if they do rest, but if they don't then I know I'll totally go back to Fort Dawnguard, clear out the bodies, and use it as my private store house.

Thanks for bringing this up! I'd like to hear more about it.