Editable Splines - Creating a letterbox

Starting with a rectangle spline I converted it to an editable spline, this option isnt available to 3D objects only splines.

After selecting the Vertex level I used the fillet option under the geomerty header.

The fillet option allowed me to move the corners of the rectangle inwards to round the top of the rectangle.

I swapped to the spline level I used the outline option to create an inner wall for my letterbox.

Which looked like this:

Using the extrude modifier brings the walls I have created out to make the base of my letterbox.

To create the back place of the letterbox I cloned the body and then deleted the inner outline I had created and adjusted the scale so it was thin and slightly larger than the main body.

After that I just aligned the body with the back place to create the letterbox.