Abstract: A security door assembly for enclosing the ends of filling and discharge hose storage tubes employed on over the road tank trucks and trailers is disclosed wherein pivotally interconnected cover door and support frame members are formed with interfitable male and female marginal lugs having coaxially aligned openings receptive of an axially moveable lock bolt whereby movement of the bolt in one direction serves to interlock the lugs and movement of the bolt in the opposite direction serves to release such lugs. A detent is provided for removably maintaining the bolt in locking and releasing positions and a stop member cooperates with the bolt to provide limited movement of the bolt in a lug releasing direction. A manually engageable member is provided on the bolt for actuating the same.