These are the magnets I plan to use on the rear door.
They fit the aluminum channel, 1 will be on the inside of the channel and the other will be recessed into the door frame.
You can see in the pic how the aluminum channel adds a nice frame for the door opening. If I would have had 2 long channels I would have run it from top to bottom, But I only had some scraps and had to splice the bottom.
And the other pic shows the inside how the door and the channel comes together. This aligns the door every time it's put on the droid.