I have a lock just like the baggage door, it is mounted so that the movable arm keeps the lower rack from moving when in the locked position. The rack simply runs into the lock arm.
For the other side, I lock from the inside with a piece of piano hinge wire, bent to look similar to a fire extinguisher pin.
I drilled a hole in the end of the inner door handle where the "push to open" tab is, goes all the way through the arm housing and the tab. Insert the pin after the copilot gets out, and lock the pilot side from the outside.