You can and should have the room secured....with this said, this will likely generate curiosity and questions. Consider having your listing agent disclose that there is a safe room area in the basement that buyer's will initially be unable to have access. At some point in the buying process, it will be necessary to make arrangements for the buyer to view this space.
Can't imagine anyone having problems with this......
I understand your concerns and they are legitimate.
Cutler Real Estate