Hi eric, here's a demo of the "draw + sweep" method.

For drawing a path directly on to a box you can use the polyline command and do the drawing in the 3D view, that looks like this:



The one tricky part is the 2nd to last point - to get that to line up with the first point I created a construction line which you do by going back to the first point and then instead of just clicking a point there you hold down the mouse button and keep it pressed down and drag away - that pulls out a construction line which you can use for various purposes like here aligning the 2nd to last point with the first point.


Then to give it thickness, you can draw a little square down flat on the ground plane away from it like this:



Select the little square and run Construct > Sweep, then select that previously drawn polyline as the path, that will build the thickened shape like this:



Then select just the main box body, run Construct > Boolean > Difference and select the thickened piece as the cutting object to get this:



- Michael