Hey guys so the last house i made failed a little bit, mainly because of the Containers deleting everything in them after a month or so. So now i'm going to worn on another house and was wondering how to make a player container 100% safe forever.

Just use the chest named "PlayerHouseChest". I think that it is perfectly safe !

Make sure that the containers you place in the house are containers where the "respawns" checkbox is not checked.

I think this is the most important setting so you can use the container that looks best in your setting. You should also be setting the Encounter Zone of your cell's http://www.creationkit.com/Interior_Data to "NoResetZone" or something safe.

Some good answers above, you can also set the owner of a container as "Player".