In the cases of Bush & Obama, those documents were/are already under the control of NARA. As per the Presidential Records Act.
Until recently, the Bush documents were in a secure warehouse waiting for the final library location to be completed. They've since been moved to their final location.
The same for the Obama papers. They're in a warehouse secured and controlled by NARA. Once the Obama Presidential library is complete, they'll be moved to their final location.
NOT in his bathroom.