Grab the Horizontal Constraint tool from the Constraints tab, and hover your mouse near the center of the bottom horizontal line until you see the green dot that signifies that a coincident constraint will be applied to the center of the line, then click. Now click on the centerpoint to apply the constraint.
Now extrude the rectangle in the negative Y direction using the Thickness parameter for the distance, to do so you will need to reverse the direction.
You should have a part like the one above now. Name the new extrusion Panel, then right click the name in the browser and suppress it. Highlight the XZ Plane in the Origin folder, then click Create 2D Sketch on the Sketch Tab. A sketch will start on the XZ, name it Profile Path. Now grab the Project Geometry tool from the Draw Tab and click all four corners of the Panel Sketch. Turn off the visibility of the Panel Sketch, and you should have four projected points and the Center Point visible. Right click and choose Finish Sketch, then save.